Implement barebones but functioning GQL server

Currently allows looking up "me", and running an availability check for
a domain name.

Remove webhooks and ACL (visibility) artifacts

They might be re-added at some point, but for now keep this focused on
the core functionality.

Start adding bits and pieces to the GQL schema

It's all preliminary for now, just to get an idea of some of the stuff
we'll need to implement.

Always keep name and extension of domain separate

Green field start for names.sr.ht GraphQL API