When a session is published, all comments in it should be considered 'notified' #2436

Fixed #2436 

btw, I think if the instructors publish session first, then they add response comments later, for this case those comments will be in the 'pending' state ('notify' button will be displayed).

Because after published, instructors/tutors may review the session and add some more comments to certain feedback. Then they'll need a way to notify students again