Sync Dataset and ProcedureDataset derived data holders

[dgasmith]

ProcedureDataset-based collections have additional features such as get_entry and get_record that Dataset-based collections do not have. At first pass we can simply add them to Dataset derivatives, but it might be worth taking a deeper look at how the class structures are evolving to make sure the drift isn't too severe.

See https://github.com/openforcefield/qca-dataset-submission/pull/36.

[dgasmith]

@mattwelborn Could you consider this issue as well as our overhaul Dataset classes?

[mattwelborn]

Can do.