Fix Bug Preventing Button Clicking

clickCallback was never called.
Add Background Music

The BackgroundMusic object will randomly wander through the list of
tracks, never repeating one.

I did not compose the music for this game, so this means lots of new
external licenses.
Add a Way OUT of the Credits Screen

A gamer's nightmare: Stuck in the credits forever.
Fix Music Credits on Windows

Haxe is sensitive to the line-endings that Git checks the file out with.
Oops! This works around the issue.
Fix null Track Crash

intRanged is INCLUSIVE.
Reduce Duplication in Background Music Code

Removes the unnecessary first randomization.