Splitting "big box" and "little box" interfaces apart (attempt #2)

[JosephCottam]

Moves the big-box interfaces into their own module and deprecates them.

[JosephCottam]

@SamWitty The failures on these tests occur on my own machine, but only sometimes. Can you look and let me know if I did something wrong in my translation to small-box interfaces?

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[JosephCottam]

@SamWitty I have the notebooks executing with the exception of one cell.

Here are notes on the choices I made:

1. The default start-state passed into setup_model was derived by the big-box function. I moved that derivation into setup_model.
2. I did not understand the 'autoguide' stuff being done, so I kept it in the notebook. This may not be reasonable in the long-run because it requires constructing a thing from the model to pass into another part of the interface BUT I don't know when to derive what (or how). We might take a 'wait and see if its a problem' approach for this one.
3. The last cell of 'demo_ensemble' notebook does not succeed where it used to. Apparently it used to get 'backcast' entries but now it does not. I'm not sure why it doesn't anymore.

Depending on how important these things are to you (esp. 2 and 3), this might be ready for merge.

[SamWitty]

Looks good. There are a few minor refactors I'd like to make, but I'll add those as a separate PR.