Removed support for the CSE168 project 1 diffuse material.  Use either DiffuseMaterial, AshikhminPTMaterial, or DiffusePTMaterial instead.
Added support for textures to existing materials.
Cleaned up warnings and commenting
Updated material instances since sampleCount is no longer a parameter of path tracing materials.  (It caused too many problems with performance for an almost non-existent quality improvement.)