Add loaders for common formats like OBJ and Collada

[philogb]

Either in IO or O3D, we would have to see.

[D1plo1d]

I've posted a non-framework-specific loader/parser to https://github.com/D1plo1d/p3d which presently supports OBJ, STL and AMF files. I'm planning on extracting a PhiloGL wrapper out of some of my code soon but it's reasonably easy to use with PhiloGL even without one.

I feel that by keeping parsers in a separate, shared repo, projects like PhiloGL and THREE.js can better focus on their core emphasis which IMHO should not be parsing the bazillion 3d model file types out there.

Pull requests totally encouraged :)