Support for multiple levels of theory in ANI2x

[chrisiacovella]

The main paper associated with ANI-2x is trained with the wB97X/631Gd level of theory.

Additional levels of theory were also computed in some subsequent papers (e.g., see https://zenodo.org/records/10108942), each stored in separate files

• wB97X/631Gd (data used to train model in the ANI-2x paper)
• wB97X/def2TZVPP
• wB97MD3BJ/def2TZVPP
• wB97MV/def2TZVPP
• B973c/def2mTZVP

The available properties in each file is a bit different (some do not include forces, some do), so the question is do we want to curate these as well?