Improvements while drafting software chapter of my thesis

[agzimmerman]

• Improve MMS interface and outputs, including formatted tables for LaTeX
• Organize mixed FE solutions and subspaces with dictionaries
• Navier-Stokes(-Boussinesq, including enthalpy-porosity) simulations assume Taylor-Hood elements. Before, the element degrees of each sub-space were independent arguments to __init__. It would still only take a few lines of code to inherit and redefine __init__ to use a different element.
• Strong residual definitions were moved to the verification test code.
• Base sapphire.Simulation class no longer has to derive from a custom class using an ordered_dict, because dicts are by default ordered in Python 3.6+. Dropped support for earlier versions of Python than 3.6
• Replaces custom sapphire.Table class with pandas.DataFrame

[agzimmerman]

Per a discussion I saw in the Firedrake mailing list, some of the current test failures (which also show up in the CRON job on master) may be related to changes in the default line search method per the changes discussed here: https://github.com/firedrakeproject/firedrake/pull/1471

Since all of the tests pass with my local build from back in March, I'm doing a new firedrake-install locally now.

[agzimmerman]

At this point in my thesis, it makes more sense to freeze the Firedrake version. I already made a Docker image (just a version of the Firedrake Docker image) which I mostly used when running Sapphire while writing this chapter here: https://hub.docker.com/repository/docker/zimmerman/firedrake