Initial skin loader implementation.

- Skins are now loaded from subdirectories of the root "Skins" directory, and can be changed in-game (but requires a restart).
- Changed the default skin directory to the osu! directory, if available.

This implements a full parser for skin.ini (excluding CTB/Mania elements) based on the current wiki information.  None of the settings have been implemented yet.

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

src/itdelatrisu/opsu/states/OptionsMenu.java

@@ -52,6 +52,7 @@ public class OptionsMenu extends BasicGameState {
 		DISPLAY ("Display", new GameOption[] {
 			GameOption.SCREEN_RESOLUTION,
 //			GameOption.FULLSCREEN,
+			GameOption.SKIN,
 			GameOption.TARGET_FPS,
 			GameOption.SHOW_FPS,
 			GameOption.SHOW_UNICODE,