Teach apt-cdrom's scoring system about non-free-firmware

I'm not sure how much that matters, but looking around in apt-cdrom's source to see how the list of components was determined, I spotted the list of hardcoded known stuff that's missing non-free-firmware. I don't think it's required, and I must confess I didn't even test that change, but I thought I'd put it on your radar anyway.

Besides that particular bit, after a quick look around, grepping for non-free and leaving doc/* and test/* aside, I think adding non-free-firmware support to at least debian/apt.conf.autoremove would make sense (we have a few firmware metapackages).