Finally removes the last of the "role" editing from PhabricatorUserEditor. There are a few rough edges here. It would be nice to move the entirety of user creation out of PhabricatorPeopleNewController, but we aren't there yet. Questions to answer:
- Should it be possible to turn existing users into bots/mailing lists or vice versa? bin/accountadmin lets you fiddle the isSystemAgent flag, but maybe that was a bad idea from the beginning.
- Are being a bot and being a mailing list mutually exclusive?
- Is it correct to require being an admin to take these actions?
- Should we just not have these transactions at all? These classes seem useful in the future where conduit is capable of creating users, and it's the last of the old "role" editing stuff, but there's also the principle of sleeping dogs.