In LoadStore, save the results of description() rather than a static transform string

This gives us robustness to one type of model file compatibility break, if
e.g. the FaceRecognitionRegistration abbreviation is changed, any results
of <FaceRecognitionRegistration> that were previously saved to disk are
not invalidated (although any changes to FaceRecognitionRegistration will
not be reflected until the model is re-trained).