Allow multiple https domains

[kennygrant]

The server should optionally support serving multiple domains over https. This would make it easier to support multiple domains in the CMS.

This should be possible using the built in packages, by using tlsConfig.Certificates and tls.Listen rather than ListenAndServe.

There can be a fallback domain, and then several other domains with their own certs that can be used if the server detects them.

We'd need some sort of setup (an array of domains) in the config, with name, aliases, cert, key rather than just the cert_file and key_file keys we have at present.