USERNOTICE, if a user unsubscribes

[cozyGalvinism]

At the moment, in order to get an accurate subscriber counter, you need to constantly call the API for it.
However, it'd be a lot easier, if all subscriptions, resubscriptions and unsubscriptions would be handled in USERNOTICE or somehow else.

This way, it'd be a lot easier to handle and the API calls on the subscriber model get a little less.