Create a docker container for the server

[Zaharid]

The NNPDF server is an increasingly complex beast and setting it up requires a pretty large amount of knowledge: ssh authentication, http authentication, SSL encryption, nginx configuration, custom indexers (see #223) , conda indexers, cron jobs, inotify and I could go on. See #469.

This also makes setting up a new server painful. It would be a lot better if we had a docker image doing all that stuff so that setting it up elsewhere (where we can run docker) is trivial with the only potential change being the DNS settings (you see how I could go on!).

[Zaharid]

Possibly the recommended (by people with too much free time) approach is to have many docker images for each service, but seems more trouble than it is worth? Anyhow, that is up to whoever does this.