Fixed bug in AspectActivity, improved Framework, and added a DepthRenderingActivity.

In AspectActivity, the constructor was calling entityAdded() before subclasses had a chance to
initialize their instance variables.  This resulted in a bug in all RenderingActivities which added
these Entities to a List for layer sorting.  DepthRenderingActivity manipulates the Camera and the
scale to create the illusion of there being a simple, layered depth; this is often used in side
scrolling platform games.