Summary:
Ref T8387. Adds new mailing list users.
This doesn't migrate anything yet. I also need to update the "Email Addresses" panel to let administrators change the list address.
Test Plan:
- Created and edited a mailing list user.
- Viewed profile.
- Viewed People list.
- Searched for lists / nonlists.
- Grepped for all uses of `getIsDisabled()` / `getIsSystemAgent()` and added relevant corresponding behaviors.
- Hit the web/api/ssh session blocks.
Reviewers: btrahan
Reviewed By: btrahan
Subscribers: eadler, tycho.tatitscheff, epriestley
Maniphest Tasks: T8387
Differential Revision: https://secure.phabricator.com/D13123
