Notification type

In those 4 files:
/phpbb/notification/type/approve_post.php
/phpbb/notification/type/approve_topic.php
/phpbb/notification/type/disapprove_post.php
/phpbb/notification/type/disapprove_topic.php

We've:
'id' => 'moderation_queue',

but it should be:
'id' => 'notification.type.moderation_queue',

Since all others kind of notification follows that naming.

I would create a PR for that since its simple, but I don't know if that will cause any kind of problems on forums that had the old id. Maybe that would ask a update to the database to fix old entries.

And at /phpbb/notification/manager.php, line 475, we've:
if ($type instanceof \phpbb\notification\type\type_interface && $type->is_available())

I had to delete the  && $type->is_available() part of it, because it was creating a problem on an extension that uses the method get_global_subscriptions(false) to get all the notification types.
With that is_Available, those types doesnt appear:

"User requiring activation:"

"Your topics/posts are approved or disapproved by a moderator:"

EDIT: This seems related to the second problem exposed above: https://tracker.phpbb.com/browse/PHPBB3-15940