Pause screen, score display, refactoring

Added text to the pause screen (slightly bugged).
Changed the score display to use the proper font. Added score background
batarang. Added bonus score popup for killing enemies.
Added game states (will probably be removed, don't think they're
actually needed).
Refactored Main.as a lot, especially relating to the plot screen and
game initialisation. Also refactored PlatformManager.as as it was
becoming unruly.