Possibly fixed BootLoaderTest build.

* Adapted to x86_64 changes.
Implemented write support, reorganized source files.

* Moved some functionality into their own files so that they can easily
  be reused by other code.
* Added crc32() function from FreeBSD. Implemented CRC handling and
  validation.
* Implemented missing write functionality.
Work in progress in getting GPTPartitionHandle working.

* Tried to use EFI::Header class, but there doesn't seem to be an easy
  way to actually hit the disk -- which we'll have to do to find out
  how large the GPT table is.
* Initialization of GPT disks is now working which is why I added the disk
  system add-on to the image. However, there is a caveat, as the backup
  header and table aren't written yet.
* Partitions can be deleted.
* Creating partitions does not work yet, but I don't know yet why; in
  theory it could already work.