OSD above fullscreen windows

[David Edmundson]

> If an application wants to hide notifications they have a perfectly
> good API for doing it.
> http://api.kde.org/frameworks-api/frameworks5-apidocs/knotifications/html/classKNotificationRestrictions.html

EDIT: We have a perfectly good API with an absolutely horrendous
implementation that doesn't actually do anything.

I'm glad this came up, at the very least need to fix this Framework
documentation.