Make our ISOs flashable to USB drives ("isohybrid")

ISOs of modern Linux distributions contain MBR and GPT partition tables in the first (usually unused) sectors of the ISO file (see Isohybrid - Syslinux Wiki for more details). This way, an ISO can be burned to a CD but also flashed to an USB drive (using DD or Win32DiskImager) and is bootable in both cases.
ReactOS ISOs should also support this to have a single file usable for both CDs and USB drives.

What should be done in my opinion:

• Importing the isohybrid tool from http://repo.or.cz/syslinux.git/blob/HEAD:/utils/isohybrid.c and http://repo.or.cz/syslinux.git/blob/HEAD:/utils/isohybrid.h
  This runs standalone when built with the option ISOHYBRID_C_STANDALONE and can just patch any ISO with the necessary MBR bytes.
• Write something like http://repo.or.cz/syslinux.git/blob/bb41e935cc83c6242de24d2271e067d76af3585c:/mbr/isohdpfx.S for FreeLDR.
• Check also that we support/implement support in FreeLDR for hybrid loading, similarly to what is done in http://repo.or.cz/syslinux.git/blob/HEAD:/core/isolinux.asm , below the magic 0x7078c0fb number (labels _hybrid_signature and _start_hybrid).

This should be the steps needed for MBR booting. The isohybrid tool also comes with GPT/UEFI support, but I'm not sure if this is enough for booting ISO-flashed USB drives on UEFI systems.