Notifications about files added in a private space

[michaelh99]

This might be related to #139 ?

If a file is added to a private space but is left as "public" (the default?), users who are not members of that space will end up receiving notifications that the file has been added. When they click on the notification, they're told they don't have access because of course, they aren't a member of the private space.

Regardless of the file privacy setting, notifications on files in a private space should only be sent to members of that space.

using 1.10.1 HH and 0.14 of the files module