Follow-up to #25.

- Moved all MultiClip-handling methods into the MultiClip class.
- Destroy extra clips when starting and finishing new beatmaps.
- Reduced maximum number of extra clips to 20.
- Attempted fixes at multithreading issues.

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

src/itdelatrisu/opsu/objects/curves/LinearBezier.java

@@ -111,8 +111,8 @@ public class LinearBezier extends Curve {
 						curPoint = 0;
 					} else {
 						curPoint = curBezier.points() - 1;
-						if(lastDistanceAt == distanceAt){
-							//out of points even though we haven't reached the preferred distance.
+						if (lastDistanceAt == distanceAt) {
+							// out of points even though the preferred distance hasn't been reached
 							break;
 						}
 					}