Django-useraudit

There is a new signal `password_will_expire_warning` and methods `should_warn_about_password_expiry`, and `days_to_password_expiry` to help with writing custom code to warn the users when their password is about to expire.

The reason why a user has been deactivated is stored now in the new `UserDeactivation` table.

Fixes:
- 15
- 16
- 17

Fixes 11

Fixes 10

Adds the `activate_user` custom Django management command to easily re-active users that have been locked out.