Add API to to inform about finished wifi scan
It would be great to have an API in libnm to be able to get notified when a wifi scan has been finished.
This is needed for Wifi selection GUIs showing a scan-indicator in order to know when to remove the indicator, see https://gitlab.gnome.org/GNOME/gnome-shell/issues/61
Reported in Bugzilla before: https://bugzilla.gnome.org/show_bug.cgi?id=795865