Fixes some in-app and documentation references to to new user
announcements and new stream announcements that were still using
'notifications' to refer them. These were missed in the original
pass for updating this language.
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.
Lauryn Menard
Steve Howell
Abhijeet Prasad Bodas
Tim Abbott
Hashir Sarwar
Anders Kaseorg