Test commission breakdown logic and arithmetic

[mikeymicrophone]

Commissions have a variety of configurations that combine cuts for co-brokers and junior agents. There are 2 or 3 specs, but more are needed to capture the breadth of the currently implemented logic.

Once it's more fully specified, we can refactor it to use a tiered split protocol that treats co-brokers and juniors in the same way, rather than having lots of specific logic about them.

[mikeymicrophone]

Testable data are generated with fabrication, and this can be used to specify all of the variants that can be handled by the protocol. Many of the variants will be quite similar to one another.