(1) `SimulationManager::startSimulation()` will check if a Viewer is
already rendering, and will only start a rendering/interaction loop
in the main thread if it isn't. This allows us to work with two
possible cases:
(a) a QT Application with an existing widget for rendering, in which
case we do not want to control the rendering window ourself in a loop
(b) a standalone `vtkRenderWindow` application, in which case we do
want to create a window when our simulation starts and loop until the
window is closed.

(2) `SimulationManager::startSimulation()` can be launched with a debug
boolean option (off by default), which will allow to not automatically
simulate the dynamics of the scene, to be able to interact with the
scene beforehand (using the mouse).

(3) `imstk::InteractorStyle` is based on vtkInteractorStyle specifically
the trackballCamera and allows to ignore mouse events in simulation mode,
and uses key events to control the simulation:
's' : start simulation
'e' : end simulation
' ' (space) : pause/run simulation

(4) The `Viewer` class and the `InteractorStyle` class have been moved
to the `SimulationManager` module, since they are more drivers of the
application themselves.

(5) The 'Sandbox' example has been refactored to make it easier to test
autonomous tests, and updated to use the new driver architecture brought
with this commit.

Also merge Utility within Core.

- SIMULATION adds the object actors and set the
interactor style to no interactions.
- DEBUG adds additional actors to visualize
lights, the camera, axis, and set the interactor
style to trackball to interact with the scene.

Light still a WIP

Adds visual tests for Isometric mapping

Changes the name of math constants to be consistent

 Adds fade background with typical paraview style bg colors.
TODO : make this a renderer setting and optional

Changes names of math constants

Uses imstk defined math constants

Adds geometry map base class and isometriMap

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

- Remove PThreads on Linux
- Correct CMake output directories in case of single
configuration type (not MSVC)

Corrects bug on Windows

Default is OFF since we have issues configuring
it on Windows currently.

All projects output directories are now common in
the top level. This commit takes care of the
CMAKE_CONFIGURATION_TYPES for Visual Studio.

With this commit the Find_XXX.cmake files do not need
HINTS anymore since all targets are built in a same
directory known to CMAKE_LIBRARY_PATH, and all headers
directories are referenced in CMAKE_INCLUDE_PATH.

The scene needs to be paused, but not the viewer.

Also make Geometry class polymorphic by making its
destructor virtual.

Conflict existed within VTK.

Can directly used to create visual objects.

Also use unordered_map in SimulationManager.

This base class was needed for storing position and
orientation of the geometries. Those global transformation
can also be applied to discrete geometries, therefore
Geometry and AnalyticalGeometry classes were merged.