docs: def move_user_data(primary, secondary):
      '''
          Moves all submissions and other data linked to the secondary user into the primary user.
          Nothing is deleted here, we just modify foreign user keys.
      '''
      # Update all submission authorships of the secondary to the primary
      submissions = Submission.objects.filter(authors__id=secondary.pk)
      for subm in submissions:
          if subm.submitter == secondary:
              subm.submitter = primary
          subm.authors.remove(secondary)
          subm.authors.add(primary)
          subm.save()
      # Transfer course registrations
      try:
          for course in secondary.profile.courses.all():
              primary.profile.courses.add(course)
              primary.profile.save()
      except UserProfile.DoesNotExist:
          # That's a database consistency problem, but he will go away anyway
          pass