1) RemoveCuller
2) Disable VBO Shift&Scale check

Also use `setUpMapper` (previously setActorMapper) more
consistently.

MeshIO (input, output, convert) for (volumetric) meshes in  .msh and .veg file format

![liverScreenShot2](/uploads/f396f4cc1570700aa9c90e835dd932d2/liverScreenShot2.png)New addition(s):
1. Added `MSHMeshIO` to read a mesh in .msh file format, and instantiate `imstk::VolumetricMesh` 
2. Added a method in `VegaMeshIO` to convert `imstk::VolumetricMesh` to `vega::VolumetricMesh`
3. Added a method in `VegaMeshIO` to write `imstk::Mesh` in .veg file format.
4. Added an example `testMshandVegaIO` in `Sandbox` to test these implementations (Attached is the output with this merge request).

See merge request !112

Improve render clock

`VTKInteractorStyle::CreateRepeatingTimer` would call
`VTKInteractorStyle::OnTimer` then sleep for the period
given in ms after calling `OnTimer` again. This isn't
adapted for rendering at a uniform frame rate, because
the time spent within the `OnTimer` function is not
taken into account in the sleep time.

By using `OneShotTimer`, we can manipulate when to
render the next frame: in (period - time spent) ms
if the time spent in `OnTimer` is smaller than the period
time, or right away (period of 0 ms) if the time spent
is over the target period (late frame).

An interface is added in the `VTKInteractorStyle`,
wrapped in the `VTKViewer`, to set the target frame rate.

Also added a commit to use `DATA_DIR` defined in the Sandbox example to easily change the data directory for each user on their own machine. Any local change to the `DATA_DIR` value should not be committed in the future.

See merge request !114

vtkInteractor::CreateRepeatingTimer would call
vtkInteractorStyle::OnTimer then sleep for the period
given in ms after calling OnTimer again. This isn't
adapted for rendering at a regular framerate, because
the time taken withing the OnTimer function is not
taken into account in the sleep time.

By using OneShotTimer, we can manipulate when to
render the next frame: in (period - time spent) ms
if the time spent in OnTimer is smaller than the period
time, or right away (period of 0 ms) if the time spent
is over the target period (late frame).

An interface is added in the VTKInteractorStyle,
wrapped in the VTKViewer, to set the target framerate.

Default value is 0ms to render as fast as possible. See:
: http://gaming.stackexchange.com/questions/221423/is-there-any-reason-to-limit-my-fps

Current default to ".". Needs to be modified for each
user on their on system (do not commit changes to this line).

BUG: Fixes wrong default value for pbd tolerance

Fixes wrong default value for pbd tolerance in PbdConstraint class

See merge request !110

Fixes wrong default value for pbd tolerance in PbdConstraint class

improve module timing

@NickMilef I quickly made this based on the way you handle frequency in the logger you created. Could you give me your thoughts on what strategy would be the best between those two?


* Current implementation: using `sleep_for`
  - **pros:** will stop the thread and will not frenetically keep looping in the while loop. (does that actually matter?)
  - **cons:** might sleep too long?

* Offered implementation: this commit
  - **pros:** as soon as `elapsed > loopDelay`, run module (won't "sleep" too long)
  - **cons:** keeps rolling in the while loop. Could that be an issue?

See merge request !108

- wrapper for loopdelay
- use double precision for loopdelay and frequency to
maintain correct values for set/get after divisions by 1000

Vtk no copy

#### ENH: Align Eigen matrix allocator for stl vectors - 0fa25818
Define `StdVectorOfxxx` for all eigen matrix structures defined in `imstkMath.h` which are used in iMSTK within a `std::vector`.
See http://eigen.tuxfamily.org/dox-devel/group__TopicStlContainers.html
Requires to update SCCD to commit 645508940 which also updates its vec3 structure.


#### ENH: Use no copy data array to map vertices to VTK - 400c0987 
Update VTK mesh render delegates (SurfaceMesh, LineMesh, TetrahedralMesh) to directly map the vertices from the eigen and stl structures in iMSTK, and get rid of `VTKMappedVertexArray`. This should considerably reduce overhead calls and improve performances thanks to the no-copy operation. See http://www.vtk.org/Wiki/VTK/Tutorials/DataArrays

Add back normals generation in the `SurfaceMesh` render delegate, and update testPbdCloth to add another row of points to the cloth (made it easier to debug the initial vertex positions), as well as adding lights to better visualize correct normals.

See merge request !107

Update VTK mesh render delegates (SurfaceMesh,
LineMesh, TetrahedralMesh) to directly map the vertices
from the eigen and stl structures in iMSTK, and get rid
of VTKMappedVertexArray. This should considerably reduce
overhead calls and improve performances thanks to the
no-copy operation.

See http://www.vtk.org/Wiki/VTK/Tutorials/DataArrays

Add back normals generationin the SurfaceMesh render delegate.

Also updates testPbdCloth to add another row of points
to the cloth (made it easier to debug the initial
vertex positions), as well as add lights to better
debug normals.

define "StdVectorOfxxx" for all eigen matrix structures
used in iMSTK within std::vector.

See http://eigen.tuxfamily.org/dox-devel/group__TopicStlContainers.html

Requires to update SCCD to commit 645508940
which also updates its vec3 structure.

VTK renaming

Renamed everything that uses VTK. Some of these classes will need an interface eventually, but that can be done as the Vulkan renderer gets built so that we can abstract the important common characteristics.

See merge request !106

Refactor physics module

**Summary**:  
*  Modifies the Dynamical objects realted classes to generalize for any problem state. This allows for rigid bodies, deformable bodies using FEM and pbd under one dynamicalObject base class.
* Adds common interface for pbd solver and FE solvers to allow simpler code in SceneManager
* Refactors all the PBD classes for bugs, style, warnings and efficiency.
* Misc. modifications including rearranging folders, example codes, renaming classes and clearing some warnings.

See merge request !103

Use HTTPS for external dependencies

As noted by @NickMilef in the developers mailing list, `googletest` git repository was using the SSH protocol instead of HTTPS, which requires users to add an ssh_key on github.com.

We switch all those external projects to HTTPS protocol, but keep the ones hosted by ourselves on gitlab.kitware.com in SSH since we might be contributing back to those during development

See merge request !105

1. Enforces style to move one line code to one line
2. Move multiple lines to .cpp
3. make epsilon part of the class
4. SolvePositionConstraint in the base class is made pure virtual

googletest git repository was using the SSH protocol
instead of HTTPS, which requires users to add an
ssh_key on github.com.

We switch all those external projects to HTTPS protocol,
but keep the ones hosted by ourselves on gitlab.kitware.com
in SSH since we might be contributing back to those
during development.

Rename NewtonMethod to NewtonSolver and the files accordingly

1. Make solve in solverBase class pure virtual
2. Rename DeformableObject to FEMDeformableObject and files accordingly
3. Efficient way to do checks in FEMDeformableObject::initialize() and pbdObject::initialize()
4. Add variable to address which map to apply for the visual geometry

Removes problemState base class
Initialize methods now return bool

Make PbdConstraint abstract base class with solvePositionConstraint to be implemted in base class

1. Template parameter in the DunamicalObject and DynamicalModel is named to StateType
2. Rename paramerts in the initialization of the pbd constraints
3. Remove unnecessary APIs in scene object hierarchy

Renames pbd constraint classes.
Renames the selfUpdate to updateGeometries

Add testing framework

Add testing with google test framework in the superbuild.

See merge request !104

Update Geometry and Sphere to have scaling and
radius respectively > 0;

With the superbuild architecture, the inner project
is not added as a subdirectory in the superbuild project,
but configured through ExternalProject_Add(). For this
reason, the CTestTestfile.cmake at the top level (superbuild
project) does not add the Innerbuild directory in which
there is another CTestTestfile.cmake referencing the tests
of the inner project.

This commit includes the file `imstkCTestAddInnerbuild.cmake.in`
which calls `subdirs()` on the Innerbuild directory. That file
is configured in the top-level build directory, and added as
the TEST_INCLUDE_FILE property to that directory. This will
include that file to the top-level CTestTestfile.cmake, which
will therefore be able to reach the CTestTestfile.cmake in the
Innerbuild directory when running ctest.

Use this commit to also only solve external dependencies
in the superbuild tree, no need to to it in the innerbuild tree.

By adding testing source files in the same directory
than the target source files, those first ones were
included in the target executables by mistake.

ctests would currently only be created for each test file,
but the GTEST_ADD_TESTS function[1] could allow to register
all gtests as independent tests.

[1] https://cmake.org/cmake/help/v3.0/module/FindGTest.html

However, that function would not allow the use of a driver
executable, since it would force the `gtest_filter` flag to
appear right after the executable name in the command, while
a driver executable would need the name of the test file
beforehand.

This commit introduces a custom version of GTEST_ADD_TESTS
where `extra_args` is called before the `gtest_filter` flag
to allow the use of an executable driver.

Note: as noted in the doc above[1], testing each gtest is
slow since they all necessite the startup of an executable.
The previous option of testing per file is therefore kept
but commented. A future focus of interest could be to
customize `add_test` to then run all gtests at once like
GoogleTest does by default.

Allows to create tests in iMSTK using google test and ctest.
Ctests are created by test files, and not by gtest functions.

Requirements:
- Requires a 'Testing' subdirectory with cpp files for each
  class to test.
- Google Test and Google Mock should be used to create unit
  tests, see the documentation below:
  https://github.com/google/googletest/blob/master/googletest/docs/Documentation.md
  https://github.com/google/googletest/blob/master/googlemock/docs/Documentation.md
- Test files should be constructed as described under\
  `imstk_add_test()` declaration