ColladaLoader: Returning a Group instead of a Scene. See #5754.
SceneLoader: The third parameter is now onProgress.
UTF8Loader: Minor clean up.
Docs: UVMapping is now a constant.
WebGLProgram: Handle envMap.mapping set to UVMapping.
Merge branch 'dev' of github.com:mrdoob/three.js into unify_loaders

Conflicts:
	examples/js/loaders/ColladaLoader.js
	examples/js/loaders/UTF8Loader.js