preflet/network: Convert ServiceView to BGroupView

* Mostly just to be consistent with everything else

Change-Id: I468ce0a20fb918ec6e696bbc9e961dbc4386d7ff
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4963
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

Network: made the revert button (somewhat) work.

* DNS add-on does not yet support it, the rest does.
* However, there seems to be some problems with the net_server when
changing interfaces -- not just with revert.

Network: moved commonly used classes into app.

* This way all add-ons share the same code, and also the same
translations.

Network: made the revert button (somewhat) work.

* DNS add-on does not yet support it, the rest does.
* However, there seems to be some problems with the net_server when
changing interfaces -- not just with revert.

Network: moved commonly used classes into app.

* This way all add-ons share the same code, and also the same
translations.