Adwaita now themes these, and a single random row of centered pixels just looks wrong.
Use an empty GtkLabel to introduce padding without the random pixels.
This is designed so power users can create virtual devices (just like in
ColorSync) that represent things like 'Hexachrome Press #2' or 'Cinema'.
This new UI isn't actually wired up yet, and there are no new UI controls as
the UI still needs love from the designers.
This was added at this point for two reasons:
1. To get the translations early so we can enable this later
2. To be able to delete the code out of gcm-prefs.c
