Uses MarginalInstance and allows an incoming model

[jrising]

This PR depends upon mimiframework/Mimi.jl#957, and consists of two main changes:

1. Allowing an existing Model or MarginalModel to be passed into create_fair_monte_carlo. The idea is that a model that uses FAIR could have other components, so we don't want to create a new model from scratch when doing our Monte Carlo.
2. We add other_mc_set(model, ii) and other_mc_get(model). The first of these is called each iteration to set any other parameters that need to be set as part of the MC. ii is the number of the iteration. The second is called after each iteration, to collect any other values of interest, which are added to an other key in the results dictionary.

Sorry that my editor removes spaces at the end of lines. Let me know if you want me to fix that.

[lrennels]

@jrising looks good to me! I will at some point add my Mimi-ified Monte Carlo functionality as well, since I have that written up for another paper in a private repo, but for now if this is working well for you I have no problem adding it in! I'll look at the Mimi PR as well.