* Add moderator role and add pundit policies for admin actions
* Add rake task for turning user into mod and revoking it again
* Fix handling of unauthorized exception
* Deliver new report e-mails to staff, not just admins
* Add promote/demote to admin UI, hide some actions conditionally
* Fix unused i18n
* Add Admin::BaseController to wrap admin area
Extracts the setting of the `admin` layout and verifying that users are admins
to a common base class for the admin/ controllers.
* Add basic coverage for admin/reports and admin/settings controllers
David Yip