Allow exporting/importing protected areas and traders correctly

[djkrose]

Right now trader areas are not treaded special in import/export.

But traders need to be registered globally, and the trader spawner needs to be set correctly for the trader entity to appear. Also the trader area protection might need to be applied differently.

Using the import/export commands it should be possible to fully copy a working trader into another location.

Also removing a trader by overwriting it with some other blocks should properly change the protection and remove and leftover trader spawner.