This should fix many issues with enchantments being lost, as the method used takes care of enchantments.
Additionally, use the new nms ItemStack constructor in places where appropriate.
Fixes (at least part of) BUKKIT-7. Need to identify any further places to fix.
Also, standardise getHandle and clean up in general.
getHandle is now using the 'entity' member variable instead of
super.getHandle, as this reduces the number of chained calls needed.