Add a chain cert

[michielbdejong]

We can probably use http://ironframework.io/doc/openssl/ssl/struct.SslContext.html#method.set_certificate_chain_file or similar.

[michielbdejong]

Right now, we're running the https server with only /etc/letsencrypt/live/knilxof.org/cert.pem and /etc/letsencrypt/live/knilxof.org/privkey.pem, we should also add /etc/letsencrypt/live/knilxof.org/chain.pem.

[samgiles]

Ah, this is easy enough to do, well spotted! We will need to use the forked Iron we have in fxbox/foxbox though to achieve this.

[ferjm]

This causes the following error on Nightly:

knilxof.org:4443 uses an invalid security certificate.