Clip.fromThree() to create Clip from Three.js AnimationClip

[ArsenicBismuth]

Just a simple utility to add more method to create ossos.Clip(), need the armature of the source model to get the bone mapping data.

[trusktr]

This is a great idea. If Clip/etc will be library agnostic though, it may need to be in a separate utility though, f.e. ThreeClipUtils.fromThree(threeAnimClip) would return a Clip. Otherwise, we'd also have to add the method for Babylon in the same class, and for Playcanvas, etc, coupling all libraries together (import Clip and you get all the rendering libraries, massive download).