Adding invited users to the notifications stream unconditionally isn't
a correct behaviour for guest users, where the previous behavior of
including the notifications stream no longer makes sense. Therefore,
while inviting a new user, the notifications stream is listed along
with other streams with a message "recieves notifications for new
streams" in order to distinguish it from other streams.
Fixes#13645.
Steve Howell
Abhijeet Prasad Bodas
Tim Abbott
Hashir Sarwar
Anders Kaseorg