protected function _getLocationTimestamp($location)
    {
        $cacheKey = 'mmi-head-ts-' . md5($location);
        $cache = $this->view->getCache();
        if (null !== $cache && (null !== ($ts = $cache->load($cacheKey)))) {
            return $ts;
        }
        //obliczanie timestampu
        $ts = file_exists($path = BASE_PATH . '/web' . $location) ? filemtime($path) : 0;
        if (null !== $cache) {
            $cache->save($ts, $cacheKey, 0);
        }
        return $ts;
    }