Backup plan for getting compound SMILES from INCHIKEY

[beasleyjonm]

Currently, nn_distance.py gets the compound INCHIKEY from Node Normalizer, then checks MolePro to retrieve SMILES. The problem is that it is impossible to go from INCHIKEY to SMILES (INCHI keys are hashed values of fixed length), so if a given INCHIKEY is not found in MolePro, you cannot get the structure.

I suggest (and will work on) a backup plan to get SMILES when a compound cannot be found in MolePro. Maybe checking PubChem or CHEBI for compound SMILES.