[MetaCyc] GIBBS-0 and STD-REDUCTION-POTENTIAL in reversible reactions

[y1zhou]

When parsing the reactions.dat file, we're matching the entries to the nodes in the graph based on the UNIQUE-ID and metaId. However, the sides in reactions.dat and metabolic-reactions.xml could be swapped, i.e. LEFT in the dat file could be Product in the SBML file.

For irreversible reactions, this is fixed in MetacycClient.fix_reaction_direction where we always assume the directions in the SBML file are true. For reversible reactions, this becomes a problem as GIBBS-0 and STD-REDUCTION-POTENTIAL could be reversed.