Moved tileCount and scale to PhysicsManager

-tileCount does not need to be part of GameManager
-Made scale member of PhysicsManager so that the scale paramter can be
removed from some functions.
Shortened GameManager::IsLevelDone()

-Removed code that checks GameState
-Removed GameManager::CountDestroyalbeTiles()
-IsLevelDone now simply returns whether physicsManager.CountDestroyalbeTiles() is zero
Added creation of Bullet to PhysicsManager

-Added Bullet speed variable to PhysicsManager
-Added function in PhysicsManager to create, init and return a new
Bullet