`topicTrackingState.forEachTracked(topic,isNew,isUnread)` can be used to
iterate through tracking state efficiently.
This is handy for extension looking at subsets of tags and categories.
This introduces a new core API to get counts per tag from topic
tracking state
This API will only be useful if a plugin enable tags in topic
tracking state using
`TopicTrackingState.include_tags_in_report = true`
* FEATURE: don't display new/unread notification for muted topics
Currently, even if user mute topic, when a new reply to that topic arrives, the user will get "See 1 new or updated topic" message. After clicking on that link, nothing is visible (because the topic is muted)
To solve that problem, we will send background message to all users who recently muted that topic that update is coming and they can ignore the next message about that topic.
