NetworkMenu: prefer wifi/3g over vpn in the panel

Wifi and mobile broadband have signal indicators and are thus
more useful than vpn icons in the panel. Therefore, in the case
we have both wifi/3g and VPN we prefer the former as the "primary
icon" and add a lock next to it.
Behavior when VPN is added to wired or other connections is still
preserved: the wired icon is replaced by vpn.

https://bugzilla.gnome.org/show_bug.cgi?id=672591

data/theme/gnome-shell.css

@@ -436,6 +436,10 @@ StScrollBar StButton#vhandle:hover
     -boxpointer-gap: 4px
 }
 
+#networkMenu {
+    spacing: 4px;
+}
+
 /* User Menu */
 
 #panelUserMenu {