Encapsulate drawing and updating of game #8
Description
To enable the game having a main menu and so on, the current draw and update should go into a new class (e.g. Layer):
The Game-Class will have a Layer-stack, that will be drawn from bottom to top. Updating should be done in two steps from the Game's perspective: "regular updates" occur for each Layer on each cycle; "focus updates" occur only for the top-most Layer (e.g. Keyboard-input)
This enables to have a game menu open, while the game continues in background.