Added the notebook and data for band gap prediction example.

beaker-notebooks/band_gap_prediction.bkr

example-data/band-gap-prediction/3366_gap_no_gap_ratio.json

example-data/band-gap-prediction/band_gaps.npy

example-data/band-gap-prediction/classifications.npy

example-data/band-gap-prediction/coulomb_matrix.npy

example-data/band-gap-prediction/energies.npy

example-data/band-gap-prediction/ids.npy

example-data/band-gap-prediction/n_atoms.npy

example-data/band-gap-prediction/sine_matrix.npy

example-data/band-gap-prediction/sorted_coulomb_matrix.npy

example-data/band-gap-prediction/sorted_sine_matrix.npy