factored MOAIProp into MOAIProp and MOAIGraphicsProp
first pass of Moai prop overlap system; added notion of overlays/underlays for rendering ad hoc layer decorations such as Box2D and Chipmunk debug lines (now that both libraries are higher level than moai-sim)
merged changes from pointinside branch
fixed merge mistake in MOAITextLabel
added basic show/hide LOD support to MOAIProp