UI Freeze exception

Hello release team,

I would like to have a UI exception for
https://bugzilla.gnome.org/show_bug.cgi?id=753786
It modifies this view:


And adds a spinner to show progress when networks are connecting, and if
there is no networks, a label to provide feedback to the user.
Also it adds networks provided by gvfs, for example the Windows Network,
which was not visible before.

Thanks,
Carlos Soriano
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