Enable serving the air:bit site over HTTPS

[fredrikhr]

Given recent developments in Web Browsers which will explicitly start flagging not HTTPS sites as unsecure and may issue warning prompts on HTML forms that point to unsecure endpoints (like we have), it might be prudent to investigate the feasability of moving the site over to HTTPS.

I propose simply using a Let's Encrypt certificate and you can probably integrate that into the Dockerfile we use.