Show the enrollment counts for each mode on the instructor dashboard.
Merge pull request #4615 from edx/dcs/enrollment_count_dashboard

Show the enrollment counts for each mode on the instructor dashboard.
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.  This adds a check before that callback gets registered.