Add a lighting pass with customization of final color computation.

src/DemoApp/main.cpp

src/libRender/CMakeLists.txt

src/libRender/RadiumNBR/NodeBasedRenderer.hpp

src/libRender/RadiumNBR/Passes/CustomAttribToColorPass.cpp

src/libRender/RadiumNBR/Passes/CustomAttribToColorPass.hpp