* Add data needed for the examples inside Sandbox
    except ETI & textures
* Remove condition on DATA_ROOT_PATH since the user doesn't have to specify it
* Rename DATA_ROOT_PATH to iMSTK_DATA_ROOT according to 267b7f72

Download Data from Girder according to data key files contained in iMSTK/Data

This uses ExternalData.cmake (Requires CMake >= 2.8.11 release).

Add TEST: Add ExternalDataTest to verify downloaded files from Girder
* Be sure the data requiered for the test is not there (delete it)
* Add the imstk_add_data(${target} ${data_list}) function in CMakeList.txt
which calls ExternalData_expand_arguments().
* It downloads the data provided by the data_list (relative path from
iMSTK/Data)

Add DOC: Add documentation on ExternalData Management
* How to add data to iMSTK from Grider
* Update data
* Use data

Add laparoscopic tool controller

See merge request !119

Also correct indentation in Pbd class.

Create a tool with two jaws and a shaft. The controller
use its DeviceTracker to update the three objects

* Rename TrackingController to DeviceTracker
* Have subclasses store a pointer to DeviceTracker instead
of inheriting it. This allows:
1. swapping the tracking controller at runtime
2. having multiple controllers control for the same scene object (eg: laparoscopic tool jaw)
* Add SceneObjectControllerBase to parent SceneObjectController
and other future object controllers
* Update tracking data only once per frame: if the same tracker
is used for multiple objects, it is updated only once per frame.
Each tracker is set to upToDate once the tracking data is updated
and offsets computed once at each frame. At the end of the frame
all the device trackers are set to be outOfDate.

Scene can be set as current in the simulation manager using the scene
pointer in addition to its name.

We know we have only 4 buttons for the Omni

Scene object controllers are now part of the scene. They are looped through
in the sceneManager to update the objects they contain.

This will allow extension to the case where multiple scene objects are
controlled by the same controller (eg: two-jawed laparoscopic tool).

COMP: Fix eigen checkout

Closes #119

See merge request !126

Eigen git tag which was currently used (e81ac4502ebbfde43a1e1761b36853d3ead47c33)
can not be checked out anymore as of Sunday, January 29 2017 for unknown
reasons, causing all builds on the dashboard to fail:

http://my.cdash.org/index.php?project=iMSTK&date=2017-01-29

error:
```
fatal: reference is not a tree: e81ac4502ebbfde43a1e1761b36853d3ead47c33
```

Add VTK rendering improvements

Closes #115

See merge request !121

DOC: Add CONTRIBUTING.md

See merge request !125

Ensure the surface mesh read will only have triangles and
no triangle strips or other cells.

DATA_ROOT_PATH is used to quickly define the root path
for all your ressources in the Sandbox example. Its value
will therefore vary for every user, which is why it should
not be commited.

This commit adds comments explaining not to commit changes
to this line, as well as how to commit part of a file only,
and displays an error when the path is not set locally.

Addresses suggestions made here:
alexis-girault/iMSTK@a63f98b5 (comment 212643)

>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8
It would be great to have the option of using pan-zoom-rotate
when simulation is running for certain applications. I keep
pressing 'S' and 'E' in succession to see if everything is good
for an example i was working on. It need not be a default run
mode option.
>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8

* Rename VTKRenderer::setup into VTKRenderer::setMode
* Add VTKRenderer::getMode
* Add VTKViewer::getRenderingMode wrapping the one above
* Consider Rendering Mode in Mouse event callbacks instead of
simulation status
* Allow to switch to Debug rendering and back with the `d` key

Press the `P` key (for "Print text", since f should be for
fullscreen) to display the rendering framerate in the left
bottom corner.

Needed to override `SetCurrentRenderer` to add the textActor.

Only update the displayed framerate value every 100ms, which
requires the variables `m_lastFpsUpdate` (last time since the
value was updated), and `m_lastFps` (to compute the framerate
value using a moving average).

When the framerate was not fixed, the next render pass
would be called using `CreateOneShotTimer(0)` while its
parameter minimum value is 1 (in milliseconds). 0 would
set it up for the default value of 10 ms.

The main bottleneck with real-time VTK rendering so far
appeared to be the normals computation. This commit addresses
that issue by making use of the latest normals computation
filter in VTK: vtkTriangleMeshPointNormals.

While this filter is much (5 to 16 times) faster than
vtkPolyDataNormals, it does not check for consistency in the
cell orientations that could cause inverted normals, which
is why the vtkPolyDataNormals is called once in the surfacemesh
renderdelegate to retrieve consistent cells for the input mesh.

See VTK merge request for more information :
vtk/vtk!2271

PS: That MR requires the latest commits from VTK master, which
does not include work made on texture wrap mode nor on multi
texture attributes yet:
- iMSTK/vtk@62a7ecd8
- iMSTK/vtk@ae373026

COMP: Fix return error in MeshIO::write

See merge request !123

System: gcc (Ubuntu 5.4.0-6ubuntu1~16.04.4) 5.4.0 20160609

error: converting to ‘bool’ from ‘std::nullptr_t’ requires
direct-initialization

COMP: Fix function is not a member of std (Win)

The merge request !117 to add custom event handlers
for vtk interaction introduced a bug on Windows, where
the <functional> header needs to be included to be able
to use `std::function`.

This fixes the 50 errors listed on cdash (due to those
`std::function` members being used frequently):
http://my.cdash.org/viewBuildError.php?buildid=1111691

PS: The experimental build for this MR did not show any
issues on CDash [1], but they appeared once merged in the
master branch (continuous). There seem to be an issue
with how buildbot runs those builds on Windows, since a
similar issue happened on windows 32 bits with Eigen
aligned data structures in stl containers.

[1] http://my.cdash.org/buildSummary.php?buildid=1111615

See merge request !122

The merge request !117 to add custom event handlers
for vtk interaction introduced a bug on Windows, where
the <functional> header needs to be included to be able
to use `std::function`.

This fixes the 50 errors listed on cdash (due to those
`std::function` members being used frequently):
http://my.cdash.org/viewBuildError.php?buildid=1111691

PS: The experimental build for this MR did not show any
issues on CDash [1], but they appeared once merged in the
master branch (continuous). There seem to be an issue
with how buildbot runs those builds on Windows, since a
similar issue happened on windows 32 bits with Eigen
aligned data structures in stl containers.

[1] http://my.cdash.org/buildSummary.php?buildid=1111615

ENH: Add custom event handlers for vtk interaction

1. Allow to set up lambda functions from `VTKViewer`
as custom behavior to run in the interactor Style
in event callbacks.
2. Simplify `VTKInteractorStyle::OnChar()` to only have
simple default behaviors (start, stop, pause, play, quit)
3. Move the implementation of `getTargetFrameRate()`,
`setTargetFrameRate()` and `setSimulationManager()` from
`VTKInteractorStyle` to `VTKViewer`, which becomes friend class
of the private members of `VTKInteractorStyle` to avoid
repeatedly wrapping around the interactor style methods.

Co-authored-by: Hina Shah <hina.shah@kitware.com> (@hina), adapted from iMSTK/iMSTK!113

See merge request !117

Fix finite element deformation models and non-linear solvers

This MR does the following:

* Fixes internal force calculation for both semi-implicit and full implicit Newton iteration
* Fixes initialization of linear and StVK material models
* Adds a modified conjugate gradient solver to handle fixed boundary conditions
* Enables damping if provided in the config files
* Enforcing code guidelines and other clean up in the related files

These fixes concludes the refactoring and bug fixes for physics module. Once these changes are merged, one should be able to create any material model with choice of semi-implicit and full implicit Newton solvers while applying Dirichlet boundary conditions. In other words, all the vega functionality (barring reduced order models) can be reproduced in iMSTK.

See merge request !118

Written-by: Sreekanth Arikatla <sreekanth.arikatla@kitware.com>

- default LinearSolver tolerance = 1.0e-4
- default IterativeLinearSolver maxIterations = 100
- remove those default values in ConjugateGradient constructor
as they are initialized in the parent constructors
- consistent use of this pointer

Written-by: Sreekanth Arikatla <sreekanth.arikatla@kitware.com>

Written-by: Sreekanth Arikatla <sreekanth.arikatla@kitware.com>

1. Implemented Homogeneous Dirichlet BC
2. changed `filter` lambda to normal method
3. simple cg solver implementation
4. return b.dot(b) instead of b.norm() within NewtonSolver::updateJacobian

Written-by: Sreekanth Arikatla <sreekanth.arikatla@kitware.com>
Written-by: Mohit Tyagi <mohit.tyagi@kitware.com>

Makes the update of LHS and RHS updateType dependent. For now only deltaVelocity type update is supported.
Clean up and renaming

Written-by: Sreekanth Arikatla <sreekanth.arikatla@kitware.com>

1. Fixs the fully implicit nonlinear Newton solver
2. Completes implementation of Newton solver that can be either semi implicit (SI) or fully implicit (FI)
3. Adds options to set the solver to either SI or FI
4. Default is SI
5. Now the lamda function computing the internal forces needs to know if it is SI or FI
6. Prints warning if the FI Newton solver does not converge within max iterations set

Written-by: Sreekanth Arikatla <sreekanth.arikatla@kitware.com>

Get rid of m_tmpStorage

Written-by: Sreekanth Arikatla <sreekanth.arikatla@kitware.com>

- use m_vegaPhysicsMesh within initializeDampingMatrix
- consider all damping coefficients

Written-by: Sreekanth Arikatla <sreekanth.arikatla@kitware.com>

Written-by: Sreekanth Arikatla <sreekanth.arikatla@kitware.com>

Written-by: Sreekanth Arikatla <sreekanth.arikatla@kitware.com>