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/Splash.java

@@ -126,11 +126,14 @@ public class Splash extends BasicGameState {
 			// initialize song list
 			if (OsuGroupList.get().size() > 0) {
 				OsuGroupList.get().init();
-				((SongMenu) game.getState(Opsu.STATE_SONGMENU)).setFocus(OsuGroupList.get().getRandomNode(), -1, true);
+				if (Options.isThemSongEnabled())
+					MusicController.playThemeSong();
+				else
+					((SongMenu) game.getState(Opsu.STATE_SONGMENU)).setFocus(OsuGroupList.get().getRandomNode(), -1, true);
 			}
 
 			// play the theme song
-			if (Options.isThemSongEnabled())
+			else
 				MusicController.playThemeSong();
 
 			game.enterState(Opsu.STATE_MAINMENU);