CI & auto-deploy

Plan:

• set up a test deployment location at test.kwant-project.org.
• set up restricted rsync users with passwordless keys that can only copy to
  • Test website
  • Actual website
• set up CI to build the website and deploy
  • To test location on any push
  • To the main location on pushes to master

The keys can be stored on the computer providing runners and mounted at .ssh/id_rsa as volumes. The runner for the test location may or may not be shared with other website users (mildly prone to abuse). @cwg, @jbweston – opinion about this last point?