Implement a new type of "Moderator" notification type for forums
This notification will be triggered also by unapproved messages. The UI will show the subscription link only to forum moderators, using a different color (customizable via css, vanilla color is red). Message content will always be hidden for such notifications, so user will need to have access to new message.
Move logics to create forum notification type to tcl to:
- reduce code duplication - make it simpler to extend forums with new notification types
This reform was triggered by a downstream request, where users would like a new kind of notification for forum moderators that triggers also when a forum message has not been approved