Introduce libvirt-l10n binary package

This is something that I've had sitting on my hard drive for about a year now, and since we're going to need a trip through the NEW queue for the next upload anyway I figured it would be the perfect time to revive it :)

I have tested the upgrade from 8.10.0-1 and it works as expected, automatically installing libvirt-l10n. I have also verified that the new package can be uninstalled without taking everything else with it, and that libvirt still works after removing it - with English-only output, of course.