Use Limine as ISO Bootloader

The ArchISO maintainer requested some feature changes at Limine to integrate it into archiso:
https://github.com/Limine-Bootloader/Limine/issues/536
https://github.com/Limine-Bootloader/Limine/issues/535
https://github.com/Limine-Bootloader/Limine/issues/537

This should make it possible in the future to use limine instead of grub for the ISO.