Add Pandas Support For Explainers

[mauicv]

Add support for Pandas data frames in any relevant explainers. (See #596)

[jklaise]

This is a more specific instantiation of #516. I think it would be great to explore adding pandas support to ALE and AnchorTabular as an initial step to understand solving the general problem. I feel like the "right" way of doing it would be to expose arguments that take user-specified callbacks doing the forward and inverse transformations required for the core algorithm to work on the agreed-upon data representation (i.e. ndarray), that way we could offer a "self-catered" solution (with some built-ins like pd.DataFrame <-> np.ndarray).