Change metabolite IDs in metabolic model file

[semiller10]

The need

Metabolite IDs should always be the ModelSEED/KBase ID rather than the current situation in which a BiGG ID can be used instead -- in retrospect this was the wrong decision, though at the time it seemed useful make the identity of the metabolite interpretable from the ID if possible.

The solution

In addition to always making the metabolite ID be the ModelSEED ID, BiGG IDs and other linked database IDs should be added as metabolite annotations.

Beneficiaries

Metabolic modelers and anyone exploring (pan)genome metabolic networks.

[semiller10]

Technical note

The ModelSEED metabolite "abbreviation" can correspond to one of the BiGG IDs. This "select" BiGG ID is currently recorded in a column added to the metabolites table that is set up from the downloaded table, but this information is no longer needed and the column should be removed.