Make weights based on item count configurable

[Zakru]

Currently, slots always have a selection weight based on their current number of items. While this is often desirable to improve variance in small samples/have a finer control of the exact block weights, there are some cases where it is convenient to simply have equal weights for all slots. For example, if you have varying amounts of the blocks in your palette, or you just want to split a stack to double its placed amount relative to the others. IMHO this should be configurable/a toggle.

Of course, there is a workaround in the case of having less of one block, which is to simply reduce the sizes of the remaining stacks. With more block types, however, more slots are being used up in the inventory for the excess.