ENH: Adds clearcoat model to iMSTK & colon fly through example rendered with clearcoat

CMake/External/External_iMSTKData.cmake

Examples/RenderingColon/CMakeLists.txt

Examples/RenderingColon/RenderingColonExample.cpp

Examples/RenderingHead/CMakeLists.txt

Examples/RenderingHead/RenderingHeadExample.cpp

Source/Rendering/Materials/imstkRenderMaterial.cpp

Source/Rendering/Materials/imstkRenderMaterial.h

Source/Rendering/Materials/imstkTexture.cpp

Source/Rendering/Materials/imstkTexture.h

...enderer/RenderDelegate/imstkVTKPolyDataRenderDelegate.cpp

...erer/RenderDelegate/imstkVTKSurfaceMeshRenderDelegate.cpp