Improve SSL setup

Would be good if someone improves our HTTPS setup

Most urgent is making letsencrypt certs renew automatically.

There's also a lot that can be done to improve the nginx config.

When I first set up the server I had gotten it to B+ but it's now at F: https://observatory.mozilla.org/analyze.html?host=social.coop

We do have a good grade on this one: https://www.ssllabs.com/ssltest/analyze.html?d=social.coop&hideResults=on

Some resources:

• https://mozilla.github.io/server-side-tls/ssl-config-generator/
• https://bjornjohansen.no/optimizing-https-nginx
• https://gist.github.com/Repox/6e7b2afdc9c11874ff3c5353f08f2974
• https://gist.github.com/gavinhungry/7a67174c18085f4a23eb