extract-iso: Extract language info

Make use of libosinfo API to extract list of supported languages.
Application (e.g Boxes) can then use this list to determine the most
suitable language to start express installation in.

https://bugzilla.gnome.org/show_bug.cgi?id=729253
extract-iso: Update copyright/author list

https://bugzilla.gnome.org/show_bug.cgi?id=729253