Use the Debian firmware package in more places
Enable the Debian firmware package on the installation CD

It's unfree but we already had such firmware on the CD so we're not
worse off.

Issue #87.
not-detected.nix: Enable all firmware

Note that since the configuration produced by nixos-hardware-scan
includes not-detected.nix, you get all firmware when following the
regular installation procedure.

Issue #87.
Typo