Model DataNode type according to Datasource BridgeDb annotation

[DeniseSl22]

Apparently adding an InchIKey as a DataSource, created GeneProducts....
Not sure if this would also happen for other datasource types for Metabolites (e.g. ChEBI, HMDB, Wikidata).
But that shouldn't happen, we could think of something smarter here (there is a world outside of genes :p)