CODE: simplified Viewer.add
CODE: render text before other potentially transparent
	objects to not occlude the text
CODE: tweaked surface coloring
CODE: simplified rendering using groups
CODE: removed broken postprocessing
CODE: removed broken orthographic camera support
CODE: dedicated transparentGroup
CODE: simplified render method
FIX: boundingbox calculation for all groups
CODE: assume surfaces generally enclose other stuff
	so they can be rendered last when transparent
CODE: properly support BackSide rendering for mesh buffers
CODE: render FrontSide and BackSide of DoubleSide transparent
	surfaces separately to avoid some artifacts