Minor formatting
Added Entity, IPhysics and Physics; Changed base class of Character to Entity; Replaced Robots property of World with Entities property; Added new Physics to LoadContent method of Game; Replaced character parameter of Begin method in IBehavior with entity parameter, refactored MoveBehavior and WaitBehavior; Moved Position and Sprites properties, Draw, Load and Move methods of Character to Entity; Removed Load overload from Sprite