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.

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