This requires the pending MR for cal_db_interactive.  Tested with e79f2c9d (current head of the
branch of that MR).

Applying isort and nbstripout.  Changing from ipyparallel to multiprocessing - and while doing so,
simplifying the call signature of characterize_module.

This metadata file subsumes the old retrieved constants YAML file.  The commit includes some refactoring centered around pathlib.