close the Mission Editor window

def close(self):
        '''close the Mission Editor window'''
        self.time_to_quit = True
        self.close_window.release()
        if self.child.is_alive():
            self.child.join(1)

        self.child.terminate()

        self.mavlink_message_queue_handler.join()

        self.event_queue_lock.acquire()
        self.event_queue.put(MissionEditorEvent(me_event.MEE_TIME_TO_QUIT));
        self.event_queue_lock.release()