Security certificates not set to auto-renew

[porld]

Security certificates need refreshing before 90-day expiry.

[porld]

This needs to be linked to the webroot of the Flask server. Previously it was done in standalone mode, which will no longer work with the latest certbot (previously only letsencrypt worked on Xenial). Last it was bodged by using webroot pointing at Python SimpleHTTPServer on 80 (temp. under sudo).

Set up cronjob, point to proper Flask webroot and use certificates directly (rather than copies).

See https://blog.miguelgrinberg.com/post/running-your-flask-application-over-https