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/SongMenu.java

@@ -253,9 +253,10 @@ public class SongMenu extends BasicGameState {
 		search.setMaxLength(60);
 
 		// selection buttons
-		float selectX = GameImage.MENU_BACK.getAnimation(1).getWidth() * 1.75f;
-		float selectY = height - GameImage.SELECTION_MODS.getImage().getHeight() / 2f;
-		float selectOffset = GameImage.SELECTION_MODS.getImage().getWidth() * 1.05f;
+		Image selectionMods = GameImage.SELECTION_MODS.getImage();
+		float selectX = width * 0.183f + selectionMods.getWidth() / 2f;
+		float selectY = height - selectionMods.getHeight() / 2f;
+		float selectOffset = selectionMods.getWidth() * 1.05f;
 		selectModsButton = new MenuButton(GameImage.SELECTION_MODS_OVERLAY.getImage(),
 				selectX, selectY);
 		selectRandomButton = new MenuButton(GameImage.SELECTION_RANDOM_OVERLAY.getImage(),