When invoked with certain arguments, show the wireless and 3g
dialogs from libnm-gtk. Previously they were provided by nm-applet,
but now gnome-shell conflicts with it and it makes sense anyway
to have one place for network configuration. Also added a "show-device"
command, that just selects a device in the tree view.
https://bugzilla.gnome.org/show_bug.cgi?id=657093
