Inventory holders are now freed from BaseInventory. They are now declared by subclasses by convention, but are not required in most cases.
Ideally, this would be followed by the removal of the need for inventories to know their holders at all. They should just be simple containers of items.
This fixes#1560 by removing FakeBlockMenu.
moving whole stacks in & out of the crafting grid works now, splitting stacks is fucked up because the transaction system can't handle the same slot changing multiple times in one transaction
