[Merge with care] Multi world inventory support.

So the concept should work, but I'm not fully familiar with the way out worlds work.

In theory this should, on world change, check their world and if its either world (Overworld) world_the_end (End) or world_nether (Nether) then set the inventory to 'survival' which is what we use currently to store all inventories.

If its not one of the three above, then load the inventory world.getName() which will load a dynamic inventory based on what world they go into. It also saves the previous inventory.

So in all theory it should work. but triple check world names and such.