implement django session-based Auth to Share authentication with backend

[danieleguido]

Documentation: Frontend served separately (same domain)

With this approach, we'll build the frontend and serve it up separately from the Django app on the same domain. We'll use Docker and Nginx to serve up both apps on the same domain locally.

See also example code

@eliselavy some steps require actions on the backend

[danieleguido]

backend: merged PR https://github.com/C2DH/journal-of-digital-history-backend/pull/178

[danieleguido]

If the user is logged in in admin, it nows output the correct username in dev vm: