Add "notify translators" link when marking page for translation

Only do this when NotifyTranslators is installed, and the actor has the
correct access.

This also needs a patch in TranslatorNotifications, as the special page has
to pick up on the passed group ID.

Bug: 49326
Change-Id: Ie3abb0411922bada6f7040699dbd8e4552eaff78
Merge "Add "notify translators" link when marking page for translation"