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/roles_controller.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+module Admin
+  class RolesController < BaseController
+    before_action :set_user
+
+    def promote
+      authorize @user, :promote?
+      @user.promote!
+      redirect_to admin_account_path(@user.account_id)
+    end
+
+    def demote
+      authorize @user, :demote?
+      @user.demote!
+      redirect_to admin_account_path(@user.account_id)
+    end
+
+    private
+
+    def set_user
+      @user = Account.find(params[:account_id]).user || raise(ActiveRecord::RecordNotFound)
+    end
+  end
+end