When a new websocket connection is established it creates a
        new :class:`ChatClient` and adds it to the set of clients of the
        :attr:`pubsub` handler.

def on_open(self, websocket):
        '''When a new websocket connection is established it creates a
        new :class:`ChatClient` and adds it to the set of clients of the
        :attr:`pubsub` handler.'''
        LOGGER.info('New websocket opened. Add client to %s on "%s" channel',
                    self.pubsub, self.channel)
        self.pubsub.add_client(self.client(websocket, self.channel))