Code style cleanup from #12.

- Moved all curve-related classes into a new package.
- Added some fields and methods to Curve abstract class.
- Removed the old (no longer used) Bezier subclass.
- Changed Error throwing to ErrorHandler.error() calls.
- Formatted code.

Also fixed a crash when reaching the ranking screen with the "Auto" mod active.

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

src/itdelatrisu/opsu/objects/Circle.java

@@ -18,9 +18,9 @@
 
 package itdelatrisu.opsu.objects;
 
+import itdelatrisu.opsu.GameData;
 import itdelatrisu.opsu.GameImage;
 import itdelatrisu.opsu.GameMod;
-import itdelatrisu.opsu.GameData;
 import itdelatrisu.opsu.OsuHitObject;
 import itdelatrisu.opsu.Utils;
 import itdelatrisu.opsu.audio.MusicController;