Add minusyz model

@taldcroft @jeanconn 

This adds the MinusYZ model to Pyger and makes it the default model to predict TEPHIN and TCYLAFT6 temperatures. 

I added a plotting function to act as a test. This function plots the max dwells for all constraints listed in the constraint_models.json file (as listed in the sim_inputs.pkl file), as well as the merged set of max dwells, using the default limits.

I used this plotting function to test the proposed 0.4.0 version against the current 0.3.0 version of Pyger. No unexplained differences were found.

These are the highlights, I made a few more small changes that are clear in the diffs and commit messages. Please let me know if you have any questions.

I plan on adding the xija version of the PSMC model in a separate pull request.