New Data Model Interfaces & LabeledDataset Class

• The Bavard in-memory data model interfaces in bavard_ml_common.types have been refactored to be in harmony with the latest.
• A new bavard_ml_common.ml.dataset.LabeledDataset abstract class has been added which can allow an arbitrarily-typed labeled list acting as a dataset to inherit nice behavior for things like cross validation, train/test splitting, and upsampling to balance by label.