Attempt making a model in CadCAD of the Vat

[ehildenb]

Using the ACT specification as a guide: https://github.com/makerdao/k-dss/blob/master/src/dss.md#vat. Another spec of the vat comes from here: https://github.com/makerdao/mkr-mcd-spec/blob/master/vat.md

Keep specially in mind:

• Is there enough information in the ACT specification to automatically generate the CadCAD model, or is more needed?
• Is there enough information in the K Vat specification to automatically generate the CadCAD model?
• What parts of the rest of the system do we need to mock to make this model usable? We likely need a price feed for Eth collateral gems to populate the Vat spot values for each ilk, and we need to mock people putting Gems into the system itself? Do we need to make difference between authed calls and not? Maybe just mock specific collateral adapters?

Goals of this exploration:

• Is it useful to generate CadCAD models from ACT specs?
• Inspect the resulting CadCAD simulation to see if we can figure out what properties are interesting about the system.