Follow-up to #68.

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>

src/itdelatrisu/opsu/GameMod.java

@@ -173,7 +173,7 @@ public enum GameMod {
 	/** The last calculated score multiplier, or -1f if it must be recalculated. */
 	private static float scoreMultiplier = -1f;
 
-	/**  */
+	/** The last calculated track speed multiplier, or -1f if it must be recalculated. */
 	private static float speedMultiplier = -1f;
 
 	/**
@@ -220,7 +220,7 @@ public enum GameMod {
 	}
 
 	/**
-	 *
+	 * Returns the current track speed multiplier from all active mods.
 	 */
 	public static float getSpeedMultiplier() {
 		if (speedMultiplier < 0f) {