Updates Item._wrapWorldEdges.
Adds _superClass property to subClass in Utils.extend.

- World extends Item
- World updates camera location in step()
- World has its own draw() method
- Item has a colorMode, life, lifespan, controlCamera property
- update Item wrapWorldEdges() method
- adds _checkCameraEdges method to Item
- System.add() checks if we're adding a World
- updates tests