Add support for notifications and libunity progress bars

This adds integration to the shell, more precisely notifications with libnotify when a process finishes and the window isn't focused and progress bars on the app icon with libunity.
Both libraries don't place dependencies, if they're not available, those features will just be ignored.
Was there a specific reason why gee-0.8 instead of gee-1.0 was used? Libunity depends on gee-1.0, that's why I bumped it now. Everything's still running fine as far as I've tested.
One additional thing that could be cool would be to display the processes name in the notification instead of a generic message.