Proposal: new 'world' methods

Requesting feedback on the usefulness of some additional `Object3D` and `Camera` methods:

	Object3D.worldPosition( optionalTarget )
	Object3D.worldQuaternion( optionalTarget )
	Object3D.worldRotation( optionalTarget )
	Object3D.worldScale( optionalTarget )
	Object3D.worldDirection( optionalTarget )

	Camera.worldDirection( optionalTarget ) // need a special one for camera...

Example usage:

    var direction = camera.worldDirection();

or, using the optional target, and avoiding `new`,

    var direction = new THREE.Vector3();
    ...
    camera.worldDirection( direction );