Real-time notifications of watched pages

We need a new Real Time / Immediate notification option, probably in Watchlist, to be able to be notified of document changes as soon as they happen.

This is very important for keeping the user informed and inside the wiki, i.e. avoid using a secondary communication channel for collaboration.

Also, it should be easy for users to change the notification method, so reusing the existing watchlist notifier option seems like the right way to go.