Allow Hearth to be stacked

Allow hearths to be "stacked" across multiple floors on the Z axis and as long as a chimney is on top they will function appropriately.

So if Floor level 1 has a Hearth, and floor level 2 also has a hearth on the exact same x and y spot of the map, then floor level 3 has a chimney at same x and y spot, both hearths would function as if they each had a chimney.