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: SSH list item now indicates a running server.

* This will be moved into the network preferences, so that it can be
used from other add-ons, as well.

Network/SSHService: Moved base ServiceView into its own file.

* SSHServiceView now subclasses it for SSH specific functionality.

Network: SSH service add-on now creates sshd user.

* If it does not exist yet, the sshd user is created upon enabling
the service.
* Also, it now uses kMsgIsServiceRunning to determine the current
label/function of the enable/disable button.

Network: first steps to an SSH service add-on.

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: SSH list item now indicates a running server.

* This will be moved into the network preferences, so that it can be
used from other add-ons, as well.

Network/SSHService: Moved base ServiceView into its own file.

* SSHServiceView now subclasses it for SSH specific functionality.

Network: SSH service add-on now creates sshd user.

* If it does not exist yet, the sshd user is created upon enabling
the service.
* Also, it now uses kMsgIsServiceRunning to determine the current
label/function of the enable/disable button.

Network: first steps to an SSH service add-on.