Parallax Background

* Added parallax background for horizontal scrolling.
General Enhancements

* Added public setters for Components.Camera .
* Changed graphics initialisation for the desktop game to run in
initialisation, not construction.
Collision Managements and SpriteBatch Extensions

* Removed old CollisionManager component.
* Added new CollisionManager node.
* Changed CollisionObject to attach itself to the CollisionManager.
* Moved DrawManager.DrawLine and DrawManager.DrawCircle to
SpriteBatchExtensions.