This re-introduces borders around the workspace buttons in i3bar.
No additional pixels will be consumed (you will not lose any space for your
windows).
In order to not duplicate configuration options and make stuff confusing, we
dropped the commandline flags (except for socket_path and bar_id). This means
that you *have to* specify bar_id when starting i3bar. The best way is to let
i3 start i3bar, which it will do automatically for every bar {} configuration
block it finds.