_mainWindowQuitHandler() {
        this._tray && this._tray.destroy();
        /*
         * NOTE: removing a certain event handler seems not to work...
         *this._window.removeListener('close', this._mainWindowCloseHandler);
         */
        this._window.removeAllListeners('close');
        this._window.close();
    }
Exit the application forcefully without raising the close event handler