Added Texture constructor in IlluminationModel

Contains a single function encapsulating the whole pipeline.
Also added mkPhongTexture to combine the stages of the pipeline.
Added portions of texture pipeline to NabRay
Changed Scene transformation map to only Proj4

It'll be easier to invert for Texture objects, and
we weren't using the generality the (Object->Object) definition
provided.
Texture mapping is go

Added special case to transformLitObject to handle appending
transformations to Textures; necessary to obtain correct mapping
to object space.
Applied red and yellow checkerboard texture to floor.