Merge branch 'VR_WIP' into 'master'

CMake/External/CMakeLists.txt

CMake/External/External_VTK.cmake

CMake/External/External_openvr.cmake

CMakeLists.txt

Source/Rendering/VTKRenderer/imstkVTKRenderer.cpp

Source/Rendering/VTKRenderer/imstkVTKRenderer.h

Source/Rendering/imstkRenderer.cpp

Source/Rendering/imstkRenderer.h

Source/SimulationManager/CMakeLists.txt

...ationManager/VTKRenderer/imstkVTKScreenCaptureUtility.cpp

Source/SimulationManager/VTKRenderer/imstkVTKViewer.cpp

Source/SimulationManager/VTKRenderer/imstkVTKViewer.h

Source/SimulationManager/imstkOpenVRCommand.cpp

Source/SimulationManager/imstkOpenVRCommand.h

Source/SimulationManager/imstkSimulationManager.cpp

Source/SimulationManager/imstkSimulationManager.h