Return original querystring but containing only managed keys

        :return dict: dict of managed querystring parameter

def querystring(self):
        """Return original querystring but containing only managed keys

        :return dict: dict of managed querystring parameter
        """
        return {key: value for (key, value) in self.qs.items()
                if key.startswith(self.MANAGED_KEYS) or self._get_key_values('filter[')}