Setup docker for deployment

[simonline]

• [ ] Configure frontend proxy including letsencrypt (and networking)
• [ ] Remove unnecessary code volumes
• [ ] Add data and upload volumes
• [ ] Setup docker environment (e.g. libre.sh)
• [ ] Setup gunicorn web server

[simonline]

We're dokku compatible now. Next steps have been added to the issue description.

[almereyda]

I have added a checkbox about setting up gunicorn above.