network: Include the connection title in the sort string

The list of networks is sorted by connection type. If a user has e.g. a
lot of VPN connections, then the unsorted list is hard to browse.
To fix this, include the title of the connection in the sort order and
ensure the list is kept sorted when a title is changed.

Reported-by: Oliver Haessler <oliver@redhat.com>

https://bugzilla.gnome.org/show_bug.cgi?id=778685