@classmethod
def templates_changed(cls, action, instance, **kwargs):
    """
        this method is called from a django signal (m2m_changed)
        see django_netjsonconfig.apps.DjangoNetjsonconfigApp.connect_signals
        """
    if action not in ['post_add', 'post_remove', 'post_clear']:
        return
    if instance.status != 'modified':
        instance.set_status_modified()
    else:
        instance._send_config_modified_signal()
