Implement an approval queue
Summary:
- Add an option for the queue.
- By default, enable it.
- Dump new users into the queue.
- Send admins an email to approve them.
Test Plan:
- Registered new accounts with queue on and off.
- As an admin, approved accounts and disabled the queue from email.
Reviewers: btrahan
Reviewed By: btrahan
CC: aran
Differential Revision: https://secure.phabricator.com/D7576