* moved Avatar::fixupModelsInScene off the newly created render thread back
to the main thread.
* updated Avatar::postUpdate to take a scene pointer, necessary for
Avatar::fixupModelsInScene
* updated developer/tests/avatarAttachementTest.js to account for recent
changes in avatar attachment scale, commit 712aff7ad.
* updated initialization of anim graph to use Model::isLoaded() instead of
Model::initWhenReady() to know when the model was completely loaded.