Consolidate Testing Data into Classes

[pbauman]

While adding testing to #240, it became clear we are starting to get some redundancy in testing data, e.g. coefficients for NASA polynomials, across testing classes. We should consolidate all this data into a class that can be subclassed so all the "gold" data is in one place. I was thinking maybe just ChemicalSpeciesData or some such (which can help with unit testing of chemical species parsing...) and then any test that needs that data can just subclass it and grab it as needed.