Seperation of Game class (META game logic) and World class (game content/logic) plus simple EventHandler

This pull seperates the game content/logic from the Game class into the World class.
* Game class contains only game meta logic like start()/end()/pause()/...
* Actual content like objects/physic can be accessed via World class

Also this pull adds a simple EventHandler (GodManipulator) that processes incoming Events.
* GodManipulator holds a pointer to the World class and so can call game content/logic manipulation during event handling.

(The other existing EventHandler is the CameraManipulator of the Viewer and called GodNavigation, it handles all events that should trigger any nagivation process like moving/rotating, just for information).