Make delay of preview animation configurable

Because the current animation preview is way too fast (30ms per frame), I've added a spinner into the animation preview panel.

It lets the user configure the delay in milliseconds (defaults to 500) for each frame/delay.

I've got no experience with jswing positioning so the position isn't in the same row as the play/pause button. If it isn't too much trouble, can you adjust it after a merge?

![capture](https://cloud.githubusercontent.com/assets/59689/2741735/c7929da0-c6f2-11e3-86d0-fc019b2ed6b8.PNG)