18/03/2010: Some refactoring and basic menu support

Time to take a step back and have a look at the overall code design ... time for some refactoring :)

1. LevelManager and Level:  both classes have been refactored to GameStateManager and GameState, since a game not only consists of levels, but also of cutscenes, menu's, interactive levels, and so on.
   
2. Game assets: the textures, fonts, video's, ... have been reorganized in the content pipeline, as such that items that belong together (eg. assets of one level) are put in the same folder:

After the refactoring, a new GameState subclass has been created: the GameStateMenu2D. That's a inheritable class that represents a game menu. A first version of it is ready, but two essential features need to be added:

1. Controller/keyboard/mouse input: without input, a menu does not make a lot of sense!
2. Bitmapped menu's: currently, the menu is dynamically created by means of two SpriteFonts and a monotone background color, but for the 'looks' I will need a cool bitmap. In fact I will need some inspiration and PhotoShop, and eventually a cool bitmap will the output :)