Shut down the entire application.

def shutdown(self):
        """
        Shut down the entire application.
        """
        if self.configWindow is not None:
            if self.configWindow.promptToSave():
                return

            self.configWindow.hide()

        self.notifier.hide_icon()

        t = threading.Thread(target=self.__completeShutdown)
        t.start()