public static function loadController($class_name)
    {
        foreach (self::$class_folders as $f) {
            $f = rtrim($f, '/');
            $filename = $f . '/' . $class_name . '.php';
            if (file_exists($filename)) {
                require_once $filename;
                if (class_exists($class_name)) {
                    return true;
                } else {
                    throw new TaskManagerException('file found but class ' . $class_name . ' not loaded');
                }
            }
        }

        throw new TaskManagerException('class ' . $class_name . ' not found');
    }