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/policies/application_policy.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+class ApplicationPolicy
+  attr_reader :current_account, :record
+
+  def initialize(current_account, record)
+    @current_account = current_account
+    @record          = record
+  end
+
+  delegate :admin?, :moderator?, :staff?, to: :current_user, allow_nil: true
+
+  private
+
+  def current_user
+    current_account&.user
+  end
+end