Introduce PhysicsManager

[bitbrain]

Introduce a new manager which allows to use Box2D in combination with GameObject instances.

For example:

Body body = getPhysicsManager()
   .newBody(new BodyDef())
   .withFixture(new FixtureDef())
   .withBody(new BodyDef())
   .withFixture(new FixtureDef())
   .withType("a game object type")
   .withMutator(new Mutator<GameObject>() { ... })
   .build();

The statement would register internally a new game object, link it to the Box2D context and automatically update the game objects data (position, rotation, scale etc.) respectively. To render the game object just use one of the existing renderers. (even animation rendering will work in combination with Box2D & Physics)