Added MainMenu State
1) Implemented first simple Main Menu
2) UIElement System started to implement
3) Added first simple state changing. Will be improved.
1) Extracted Resource Cache class
2) added some getter-Methods for simpler usage
3) simplyfied rendering in GameStates
1) Removed warnings
2) dispose all resources on game quit
1) fixed warning
Merge branch 'master' of https://github.com/Leopard2A5/XFTL.git