Follow-up to a6ece30: allow changing volume anywhere with ALT key.

The master volume can now be changed (using the mouse wheel) with the ALT key pressed in any menu, as in osu!.

Also improved the handling of dimmed tracks.

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

src/itdelatrisu/opsu/states/MainMenu.java

@@ -418,6 +418,13 @@ public class MainMenu extends BasicGameState {
 			downloadsButton.resetHover();
 	}
 
+	@Override
+	public void leave(GameContainer container, StateBasedGame game)
+			throws SlickException {
+		if (MusicController.isTrackDimmed())
+			MusicController.toggleTrackDimmed(1f);
+	}
+
 	@Override
 	public void mousePressed(int button, int x, int y) {
 		// check mouse button