public static function includeConfigFile($filename, $application = null)
    {
        if (empty($application)) {
            $application = Yii::$app;
        }
        $appKey = UniApplication::appKey($application);
        if (!isset(self::$_configFiles[$appKey][$filename])) {
            if (is_file($filename)) {
                self::$_configFiles[$appKey][$filename] = include($filename); // var $application can be used in $filename
            } else {
                throw new InvalidConfigException("Config file '$filename' required");
            }
        }
        return self::$_configFiles[$appKey][$filename];
    }