refactor websocket to support other real-time stuff

[bunop]

Is your feature request related to a problem? Please describe.
Websocket could be refactored in order to support other real time stuff, for instance zooma calls: I could display a progress bar, or I could activate or deactivate action buttons relying on completed task or missing terms

Describe the solution you'd like
By refactoring websocket I could support other types of request and will be more easier to maintain and add other features. Code could be tested with appropriate methods.

Describe alternatives you've considered
Things could remain the same and informations between frontend and backend could be managed using JavaScripts and django views. However, since we have websockets implemented we could exploit better this resource and add additional features

Additional context
Some useful links to understand better before to decide a plan:

• writing tests for async functions
• celery progress bar here, here and here (useful to display tasks status)
• other progress bar
• spanish django channel rest
• rest and channels
• documentation on django channels (channels intro)
• async notification
• sending messages
• channels and progress indicator and a docker-composed project