Two commits:
- postgresql: Use Person.from_fullname if name and email are None
- Mostly use normalized Person objects in tests
The first commit allows us to populate sensible name and email values out of the
new displayname field, without having to store them.
The second commit opens up the possibility of eventually ignoring the name and
email fields stored in database in favor of parsing them again from the
fullname field (and therefore to update our parsing logic without having to
affect stored data).