Beatmap downloader improvements and fixes.

Updates:
- Added some buttons to downloads menu: clear inactive downloads, import beatmaps, reset search, and show/hide unranked maps.
- Small changes to OsuParser, OszUnpacker, and OsuGroupList (mostly adding return values) to allow parsing only newly unpacked beatmaps.
- Added alpha fade hover effect to MenuButton, as an alternative to expanding (used for 3-part menu buttons).
- Added text rendering fields to MenuButton (also for the 3-part menu buttons).
- Added sound effects to downloads menu.

Fixes:
- Check downloads for illegal filename characters, and remove them if necessary.
- The number of results and downloads shown now supports all resolutions.
- Confirmation dialog no longer appears when restarting the application (since downloads are static).
- Do not set a focus node immediately if the theme song will be played.
- Always play the theme song if no songs are loaded (even if disabled in settings).

Signed-off-by: Jeffrey Han <itdelatrisu@gmail.com>

src/itdelatrisu/opsu/states/Game.java

@@ -730,7 +730,7 @@ public class Game extends BasicGameState {
 			restart = Restart.FALSE;
 		}
 
-		skipButton.setScale(1f);
+		skipButton.resetHover();
 	}
 
 //	@Override
@@ -806,7 +806,7 @@ public class Game extends BasicGameState {
 		skipButton = new MenuButton(skip,
 				width - (skip.getWidth() / 2f),
 				height - (skip.getHeight() / 2f));
-		skipButton.setHoverDir(MenuButton.Expand.UP_LEFT);
+		skipButton.setHoverExpand(MenuButton.Expand.UP_LEFT);
 
 		// load other images...
 		((GamePauseMenu) game.getState(Opsu.STATE_GAMEPAUSEMENU)).loadImages();