Makes the given user a tutor.

def make_tutor(user):
    '''
    Makes the given user a tutor.
    '''
    tutor_group, owner_group = _get_user_groups()
    user.is_staff = True
    user.is_superuser = False
    user.save()
    owner_group.user_set.remove(user)
    owner_group.save()
    tutor_group.user_set.add(user)
    tutor_group.save()