Just require hostName and domain instead of an extra publicIPv4 option.  Leave
behind a similar option, `publicAddress`, just in case it needs to be
overridden at some point, but stop supplying a value for it anywhere.

Put its contents in it and then use them from there instead of importing them
all over the rest of the code.

For consistency reasons: Even if they had a perfectly good swap
partition already, and also for AWS hosts.

The default case was actually catastrophically bad for any actual deployment
since it would just lock everyone out of all the systems.

More flexibility and less dots in config files.
Implements #65.

Discern make-issuer.nix from issuer.nix better.

The IP address is given as an argument

Also configure a new value on the staging grid

Also put library code in a library directory