make watching searches work

Idea

 

C.W. Gabel Trefz watched Wagn News, probably (and understandably) presuming they'll get emails when a new news item is posted. Of course they won't. They will if they watch Blog entry, but that's not obvious.

 

Given our current notification is triggered at the moment a card is edited, do we check which Search results are changed by each card edit, and send notifications to people watching cards which have the edited card as a new result?

 

 

+relevant user stories