Fixes:
- Set the modified speed again after unpausing and loading from checkpoints.
- Changed countdown delays based on current speed.
- Changed color of highlighted song info text to that in osu!.
- Made playback images unskinnable.
Code changes:
- Changed playback field in Game class to the PlaybackSpeed object instead of just the button.
- Changed PlaybackSpeed.next() to a non-static method.
- Added/edited Javadocs.
- Changed image names.
Signed-off-by: Jeffrey Han <itdelatrisu@gmail.com>