Add moderator role and add pundit policies for admin actions (#5635)

* 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

app/controllers/admin/suspensions_controller.rb

@@ -5,11 +5,13 @@ module Admin
     before_action :set_account
 
     def create
+      authorize @account, :suspend?
       Admin::SuspensionWorker.perform_async(@account.id)
       redirect_to admin_accounts_path
     end
 
     def destroy
+      authorize @account, :unsuspend?
       @account.unsuspend!
       redirect_to admin_accounts_path
     end