Materials should be in their own layer

[drwave]

In order to correctly represent face color from SketchUp in USD, I really need to make a Material to do this. Best practice seems to indicate that I should have a shader graph at the top of the scene that can serve as a fallback to map displayColor to the color3f inputs:diffuseColor and float inputs:opacity to displayOpacity.

For debugging, and just general clarity, I should write these to their own layer.