Add support for mentions in comment fields

Ckeditor Mentions Notifications now work with comment entities.

An optional setting was added to fetch values from the parent entity instead of the comment itself.

Please review when possible.

I was not able to apply this patch to either the 1.0.1 or the dev version.

@bhogue sorry, you need to first apply this one 🐛 Typo in ckeditor_mentions_notifications.settings.yml filename Active

@introfini I see the new option to "Use parent entity for comment tokens," but I am not able to mention another user. Both users have enabled comment notifications. I don't see any text format filter active.

@bhogue have you given those users the permission "User can access other user Real Names for @mentions (protects AJAX callback path)"?