Add method for handling channel change

[StevenMapes]

Is your proposal related to a problem/issue?

feature

Description

At the moment the channel is set via the querystring when you connect to the websocket without a way to change it. Create a method to handle changing the channel via a specific "action". It should just be:

    def change_channel(self, request, *args, **kwargs):
        """Update the channel the user is connected to"""
        self.websocket_session.channel_name = self.body['channel']
        self.websocket_session.save()

or something similar. This will allow a user to jump between channels