More graphical updates, some code cleanup, and minor fixes.

- The MenuButton class now fully supports hover effects (scale, fade, rotate) for Animations.
- Used a fixed location for the selection buttons in the song menu (previously based on the "back" button width, which varies widely in different skins).
- Added hover effects for "retry" and "exit" buttons in the ranking screen.
- Changed animation speed of back/skip buttons.
- Fixed a bug where main menu showed the incorrect number of songs loaded during searches.
- Removed unneeded draw() methods in Utils for color filters (since 69f5aa5).
- Moved Utils.drawCentered(Image, ...) into the Image class.
- Added overwritten Image class to Maven excludes.

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

src/itdelatrisu/opsu/states/MainMenu.java

@@ -236,7 +236,7 @@ public class MainMenu extends BasicGameState {
 		g.setFont(Utils.FONT_MEDIUM);
 		int lineHeight = Utils.FONT_MEDIUM.getLineHeight() * 9 / 10;
 		g.drawString(String.format("Loaded %d songs and %d beatmaps.",
-				OsuGroupList.get().size(), OsuGroupList.get().getMapCount()), marginX, marginY);
+				OsuGroupList.get().getMapSetCount(), OsuGroupList.get().getMapCount()), marginX, marginY);
 		if (MusicController.isTrackLoading())
 			g.drawString("Track loading...", marginX, marginY + lineHeight);
 		else if (MusicController.trackExists()) {