Add benchmarks for interaction fingerprints

[ncfrey]

This PR adds scripts and benchmarks for predicting binding affinities from PDBbind using interaction fingerprints (via RdkitGridFeaturizer) and random forests / fully-connected networks.

Notes on the benchmark:

• The benchmarking runs are pretty slow because of the large fingerprint sizes (easy to get OOM errors here) and the combinatorics of different things to try, so I changed some inputs to give smaller fingerprint vectors and tested all combinations of R^2 and RMSE metrics, RF vs fully-connected network models, and Voxelized ECFP vs Ligand ECFP fingerprints.
• Unsurprisingly, optimized AtomicConvs outperform all of the above combinations. Optimizing the ECFP settings could almost certainly boost performance further, but I stuck with default settings.

CCing @rbharath @mufeili

[ncfrey]

Thanks @mufeili for the detailed review! I have addressed the comments above.

CCing @rbharath

[ncfrey]

Closed by #34