Encapsulated Game, Intro and BackgroundBall

Created classes for Game, Intro and BackgroundBall and cleaned up /
reduced global variables.

There's still a lot to do:
- Implement level change, game over (possibly bonus level from original
game?)
- Implement more control options (mouse, LEAP motion)
- Change / cleanup jumping algorithm
- Level selection / loading / activation in editor
- Cleanup and document code
- Fix plenty of bugs