'Add a registration request for the user.
:rtype : RegisterUser'

def add_registration(self, username, first_name, last_name, email, password=''):

    register_user = self.appbuilder.sm.add_register_user(username, first_name, last_name, email, password)
    if register_user:
        if self.send_email(register_user):
            flash(as_unicode(self.message), 'info')
            return register_user
        else:
            flash(as_unicode(self.error_message), 'danger')
            self.appbuilder.sm.del_register_user(register_user)
            return None
