Set up placeholders for when WebGLSprites don't have their raw data built yet. Not finished yet because of scaling, but will come back to it... Got some refactoring to do first.
Refactored WebGLSprite to SegmentedSprite and SingularSprite, and refactored renderStrategy (container/spriteSheet) to spriteType (segmented/singular).
Renamed WebGLLayer to LayerAdapter.