DNS as code

[lgarron]

Moved from: #3

I'd love to use something like OctoDNS so that we can switch DNS providers whenever we want. Then it's very clear how to handle DNS changes (and how to make/propose changes), and it matters rather little in practice which service actually serves the DNS records.

Ideally, this would be tied to deployment automation (#4) so that we can create new domains with very DRY code changes.