add timeout errors in search_multiple_requests

searx/search.py

             remaining_time = max(0.0, timeout_limit - (time() - start_time))
             th.join(remaining_time)
             if th.isAlive():
+                result_container.add_unresponsive_engine((th._engine_name, gettext('timeout')))
                 logger.warning('engine timeout: {0}'.format(th._engine_name))