Removed custom VarInt/VarLong solution.
Moved itemstack and fluidstack serialisation to their own NBT tag to avoid interference.
Removed now useless NBT sorting
Added NullItemList
* Use itemstack as itemdef
* HIGH_TAG/LOW_TAG should be compared both directions
* Remove getTagCompound
* Make Itemlist implementation independent
* Cache item id for performance reasons
* Add preconditions to saveguard against external meddling
* Chache itemDamage
* Remove IAEStackSearchKey for now, rename getDisplayStack