[gpt] add support for GPT partitioning and EFI boot

* Contains the bulk of the code required to address #11
* Tested with Windows 8 Pro x64 (en-gb_windows_8_x64_dvd_915412.iso)
  and Arch Linux (archlinux-2013.01.04-dual.iso) against an UEFI 2.1 BIOS
* Also fixes missing status report beta versions check