Require confirmation by email for manager changes
It doesn't make sense that anyone can add themselves as a manager of anyone else. This change adds an email confirmation step for creating a relationship, as well as some more general changes for working with email confirmation of other events in the future.
Requires configuration of SMTP server for it to work.
- Database for tokens associated with deferred actions
- Adding manager or subordinate optionally requires confirmation from second party by email.
- Celery notification task to send confirmation emails
- View for activating token actions
- Modal alert in the user facing UI