Support preservation of metadata in superblock

[JayFoxRox]

When exporting and re-importing a FATX filesystem, some metadata from the superblock will be lost.
On XMUs this contains the nickname of the device.

Such data should be exportable, and re-importable.

Somewhat related to this issue, additional options should potentially be investigated, like preserving accurate flags for each file entry, or even FAT allocations (offsets of files), list of broken sectors etc., ... (could be realized by exporting a python script which uses the FATX-on-a-snake API to re-add all the file contents again - so it would be a human readable script with one-line per file); however, this issue is primarily about the superblock.