Migrate live-usb-loader.sh to extlinux and create a non-overlay user storage file system
Users should have a user storage file system, but an overlay file systems can break the boot process if it becomes corrupted due to accidental device unplugging.
This patch set implements user storage as a secondary partition that does not overlay the USB Trisquel install.
With this script it is possible to write directly to a physical drive or to write to a disk image opened with losetup.