Improve and expand DNS data

We were storing some TTL values and CNAME values if present.

I've added:
* recording of IP addresses and TTLs from A records
* detecting AKA domains
* showing this on the Site show page

It is worth noting that the TTL we store is whatever the nameserver (Google in this case) has at the time we ask. What we really want to know is the highest value, for which you need to ask the authoritative nameserver. I couldn't see how to make ruby do this without shelling out to `dig`. Redirector has a script for doing this with this command: `dig @8.8.8.8 +trace foo.gov.uk`. In practice though, the value we are recording is generally good enough for telling whether it is set low enough (ie 5 minutes) or not. This can be iterated on.

![screen shot 2014-03-06 at 10 31 12](https://f.cloud.github.com/assets/93739/2344103/861055d8-a51a-11e3-9f5b-6fcff984e488.png)