Tweaked 2d Physics body creation, exposed more Box2D features to the engine

- Creation of physics bodies now respect any compound tranformations of
a ScreenEntity
- PhysicsScreenEntity can now change angular and linear damping,
friction, density, and collision category and masks.
- Collision only PhysicsScreenEntity's can optionally be set as not a
sensor, so contact information is preserved in the manifold. collisions
are still disabled before they hit the solver.