Automatic workload-based slots at studio level

[zkat]

We should have an option, either on top of or instead of our current strategy of commission closure management where we do things at the studio level. This is reasonable because studios themselves can only take so much work, and accepting one large commission necessarily means they can do fewer of other commissions.

My proposal is that we let studios assign "slot points" to their studio that define how much total work a studio is able to put in at a time, or over a period of time.

They would then go into every offering and, instead of setting the number of slots, the studio would set the number of offering points per commission, and "slots" would be calculated automatically from there.

[zkat]

Bumping up the priority because this seems to be the most wanted next-big-feature right now.