NetworkMenu: actually add new access point to the network list

Previously the code in _accessPointAdded was iterating over the
the network list to find a good place, and at that time, added both
the network to the list and the item to the menu. When I refactored
to call queueCreateSection, I forgot to add code to insert the
network in the list.
Add it now, using the new Util.insertSorted function.

https://bugzilla.gnome.org/show_bug.cgi?id=666429