Add Parameter Range Testing

[JamesPHoughton]

One of the most straightforward tests of any model should be to check that none of the variables go outside their plausible ranges. Vensim does this automatically when you put in values for min and max in the model editor. We should be able to replicate this ability, and perhaps extend it by allowing the user to sweep over the plausible parameter space and check that values are consistently within the allotted bounds.