Since ConfigurationSerializable, there's no need to manually serialize
items anymore, and thus we let Bukkit serialize player inventories for
when players join arenas.
However, the "repairables" in the soft-restore mechanism still use the
now obsolete SerializableItem and SerializableInventory classes, and
should perhaps be rewritten.
Note that for 1.0, it may still be necessary to write a custom means
of serializing items, since we don't know if a given implementation
supports native serialization (however it should be possible to rely
on Bukkit's in the Bukkit-specific classes).
Andreas Troelsen
ffe270511c