public static function getAssetsUrl($forceCopyAssets = false, $cdn = false)
    {
        if (!isset(static::$assetsUrl)) {
            if ($cdn) {
                static::$assetsUrl = '//cdn.jsdelivr.net/foundation/4.3.1/';
            } else {
                $assetsPath        = static::getAssetsPath();
                static::$assetsUrl = \Yii::app()->assetManager->publish($assetsPath, true, -1, $forceCopyAssets);
            }
        }
        return static::$assetsUrl;
    }