Added oncomplete signal

[agoemans]

Added onComplete signal which is dispatched when animation ends.

[NeoHoffa]

@agoemans / @AleBles ,

I have a request. Can you also add an onEnd signal as well that gets called when an animation is finished playing completely? The onComplete signal is great, but it gets called each time of the animation is looping.

My current work around is to do the following, but doesn't seem like the best use:

spine.state.tracks[0].onEnd = function() {

}

Or perhaps simply passing true or false to the onComplete signal dispatch to tell if the animation is currently loop or not.

spine.onComplete.add( function(isLooping) {
        
}, this);

Thoughts? Thanks!

[AleBles]

@NeoHoffa, sure no problem