TextField updates, and bug fixes from some recent commits.

- Added modified copy of slick.gui.TextField: added CTRL+BACKSPACE for word deletion, and disabled left/right arrows to move cursor and CTRL+Z to undo.
- Fixed musicEnded() incorrectly setting the "trackEnded" upon swapping tracks.  This has caused some nasty loops since #38.
- Fixed a null pointer exception in OsuDB from 0b03912.
- Fixed the song menu search bar transition being incorrectly reset when hitting backspace on a 0-length query.

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

src/itdelatrisu/opsu/audio/MusicController.java

@@ -111,7 +111,10 @@ public class MusicController {
 			player = new Music(file.getPath(), true);
 			player.addListener(new MusicListener() {
 				@Override
-				public void musicEnded(Music music) { trackEnded = true; }
+				public void musicEnded(Music music) {
+					if (music == player)  // don't fire if music swapped
+						trackEnded = true;
+				}
 
 				@Override
 				public void musicSwapped(Music music, Music newMusic) {}