Updated custom item sell 5

[BUGFIX] fixed bug #4
[BUGFIX] fixed bug #5

[BUG] Player death will drop all items, even if stolen ones are removed and put in stolen to claim. This duplicates stolen items. see bug #7

-- Code related
[CLASS] Renamed ShippedSerialization to ClassSerialization. Now this class helps with serializing other "temp" classes like RSPlayerInventory.