Check if user is anonymous before calling PSYCHOMETRICS

LTI grade callbacks for example, come in with an anonymous user.  This causes a
stack trace in the psychometrics app that leads to the LTI service
getting a 404 when trying to grade.  This adds a check before that callback gets registered.


Good point, I had grabbed that from another piece of code, and hadn't thought of using mock instead of the django settings override. I've also rebased