Use APT::Sources::With for language packages and other extras (grub2-fll-portable)

[kel-mo]

• Generate an apt.conf file with a bunch of 'APT::Sources::With:: "/path/to/foo.deb";'
• Avoids a building a repo and especially a Release file and a sources.list entry and so also time issues
• What it does is basically making all the debs their own virtual repo that is trusted=yes
• Use apt install pkg-from-l10n-repo' as before (just with a "-c|--with-source /tmp/myl10ndebfiles.conf" added)

[kel-mo]

Depends on https://github.com/fullstory/pyfll/issues/3 and https://github.com/fullstory/fll-live-initscripts/issues/1

[kel-mo]

b4ba833 and af41586