Upgrade to flixel 3.3.1
- Remove nextState member in FlxSplashPlus to use FlxSplash's instead
- Remove FlxPlus.getMusicTime as you can now access FlxSound.time
- Modify FlxPlus.playPersistingSound for survive -> persist change
- Add a completely useless FlxPlus.delay function
- Modify FlxPlus.tempChangeTimeScale to use FlxPlus.delay, and only
  reset FlxG.timeScale to 1.0 if no callback is given.
- Modify FlxG.sleep to actually sleep the game, and not just hackysleep
- Some miscellaneous commenting / making things lok nicer.