Fix up several fields in the admin UI for models.
While adding some entries to the docs database for the diff file

attachments, I realized we had some missing fields in the admin UI and

some fields that should have been limited to raw IDs. The file

attachment fields on ReviewRequest weren't exposed at all.
This change adds the missing fields and marks up a few to require raw

IDs.
Also, some fields weren't allowed to be blank, even though they should

have been.

I was able to add what I needed to the database.