Refresh list of interfaces

I see two options:
- add a button to the menu that lets the user refresh the list manually
- refresh it automatically when interfaces change

The second option only works if GTK allows to somehow listen to changes in the interfaces. Does anyone know whether there is an event or signal for that?
We could also poll periodically, but that's really not ideal.

Start by investigating the interface-list refresh path and whether GTK exposes an event or signal for network-interface changes. Compare that with the manually triggered refresh and periodic polling options described in the issue; the work is done when one supported refresh approach is selected and implemented.

Written by the indexing model from the issue text.