This commit exposes some inner variables of notifications.js to make
them easily testable. The first test added simply checks whether the
showing and closing of notifications works properly, and doesn't yet
verify the main code logic of the notification generation.
We create a node unit test,
with 'muting' and 'stream_data' modules as dependencies,
to test the logic in notifications.message_is_notifiable.
Part of #2945
Tim Abbott
Rohitt Vashishtha
Steve Howell
Catherine Kleimeier