By removing mutable state in VolumeWiiCrypted, this change makes
partition-related code simpler. It also gets rid of other ugly things,
like ISOProperties's "over 9000" loop that creates a list of
partitions by trying possible combinations, and DiscScrubber's
volume swapping that recreates the entire volume when it needs to
change partition.
Rather than rely on the developer to do the right thing,
just make the default behavior safely deallocate resources.
If shared semantics are ever needed in the future, the
constructor that takes a unique_ptr for shared_ptr can
be used.
JosJuice