Minor updates.

- Draw the playfield background in the song menu if a background cannot be drawn for the focused beatmap.
- Added ScoreDB.deleteScore() method to delete a score from the database.
- Added @author tags for curve-related classes (by fluddokt, #12).

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

src/itdelatrisu/opsu/states/Game.java

@@ -177,6 +177,7 @@ public class Game extends BasicGameState {
 			Image playfield = GameImage.PLAYFIELD.getImage();
 			playfield.setAlpha(dimLevel);
 			playfield.draw();
+			playfield.setAlpha(1f);
 		}
 
 		int trackPosition = MusicController.getPosition();