Add a files-interface

[tomaka]

Would allow:

• Enumerating the list of disks.
• Enumerating the list of partitions on a disk.
• Reading/writing files by passing a disk, a partition, and a file path.

This interface wouldn't expose a "global file system". Instead, accessing a file requires explicitly specifying which disk partition we're targeting. I don't want anything magic happening.

Similarly, if a file system for example doesn't allow storing permissions, then we should explicitly report that permissions aren't supported.

This interface would not be accessible by regular programs, as it is too dangerous.