Fix perf issue with onFinish callbacks
Internally, to fire a provided onFinish callback, I was binding a listener to the transitionEnd event. Negligently, I forgot to un-bind that listener once the transition completed!
This means that each animation incremented the number of times the onFInish callback was executed - not good at all.
Credit to @IamNotUrKitty to finding, testing, and fixing the issue =D