Integrate Bullet Physics Engine

[perandersson]

Create a Bullet Physics Engine (http://bulletphysics.org/) specific implementation of the IPhysicsProcessor.

Questions that needs to be answered:

1. On what level should the physics engine be placed. Game-, Scene- or SceneGroup level.
2. Integration with current collision algorithms.
3. Positioning and Collision components

[perandersson]

2. Integration: Since the frustum culling used by the rendering engine doesn't require a precise polygon collision it's better to let the rendering engines collision algorithms be left alone. It's much cheaper to let the existing deferred render pipeline to remove non-visible items instead. This might be changed in the future.