Missing implementation of the CLSID_UserNotification / IUserNotification interface for shell notifications

As far as I can see in our current code (r74448), we don't have implementation of the CLSID_UserNotification / IUserNotification interface for shell notifications, that display balloons, as described in:
http://stackoverflow.com/questions/6270539/how-to-shell-notifyicon-without-adding-an-icon-in-the-notification-area
and an example given in:
https://github.com/ma-vysotskiy/reminder.tray/blob/master/Reminder.h

This functionality could be useful for implementing the balloon popups for hard errors.

Cc Smiley