Add Django Channels integration to example app

[tim-schilling]

Django Channels is an async library for Django that has a tutorial about building out a chat application. It's a common websocket interface. We should add that to our example app for easier manual testing. It would also serve as a way to prove that Debug Toolbar works with Django Channels

https://channels.readthedocs.io/en/latest/tutorial/index.html

References: #1413

[Chiemezuo]

Hi @tim-schilling
I would like to take a stab at this. Is there a particular way you would like it to be done in the example app, or still just a chat application?

[tim-schilling]

@Chiemezuo I think the async, websockets chat app would be excellent to integrate into the example/async_ app