Half merged the extendified_notify applet.
Receipt and display of notifications is working, although I've temporarily disabled actions.

Still to do:
* Get actions working again
* Allow closing of a notification without having to drag it away and close it as a regular applet
* Implement timeouts and other cases where a notification is closed without user interaction
* Figure out what to do about saving/restoring notifications across plasma restarts - especially when the notifying app is no longer running