Slave cost map project

Per my musings in !9276 (merged), begin tweaking slaveCost() to be a bit more transparent. Right now, all this MR does is allow slaveCostBeauty to return a map. slaveCost() is the only thing that uses slaveCostBeauty(), conveniently, meaning I only had to make one small change there and it returns a number like normal.

However, we could call slaveCostBeauty in a second place, and get the info that map provides: