ENH: Added custom mapper class and restructured light classes

Base/Geometry/Mesh/imstkMesh.cpp

Base/Geometry/Mesh/imstkMesh.h

Base/Geometry/Reader/imstkAssimpMeshIO.cpp

Base/Materials/imstkRenderMaterial.cpp

Base/Materials/imstkRenderMaterial.h

Base/Materials/imstkTexture.cpp

Base/Materials/imstkTexture.h

Base/Rendering/CMakeLists.txt

...endering/RenderDelegate/imstkVTKCapsuleRenderDelegate.cpp

Base/Rendering/RenderDelegate/imstkVTKCubeRenderDelegate.cpp

...ndering/RenderDelegate/imstkVTKCylinderRenderDelegate.cpp

...ndering/RenderDelegate/imstkVTKLineMeshRenderDelegate.cpp

.../Rendering/RenderDelegate/imstkVTKPlaneRenderDelegate.cpp

Base/Rendering/RenderDelegate/imstkVTKRenderDelegate.cpp

Base/Rendering/RenderDelegate/imstkVTKRenderDelegate.h

...Rendering/RenderDelegate/imstkVTKSphereRenderDelegate.cpp

...ring/RenderDelegate/imstkVTKSurfaceMeshRenderDelegate.cpp

Base/Rendering/VTKShaders/mesh.frag

Base/Rendering/VTKShaders/mesh.vert

Base/Rendering/imstkVTKCustomPolyDataMapper.cpp