NCBI is phasing out sequence GIs

We should check if this breaks anything for us.

https://www.ncbi.nlm.nih.gov/news/03-02-2016-phase-out-of-GI-numbers/

TL;DR:

• Always use accession.version.
• New records will no longer be assigned a GI number.
• GI numbers will no longer be included in the GenBank format.
• Querying by GI number will remain possible where it is now.
• Services that currently only support querying by GI number will support querying by accession number.

Here's another place where we use a GI number in the Entrez API. I'm not sure if this will be a problem, but at the moment that's the only thing returned for this call by Entrez (no accession number), so we can't change it (yet).

The geninfo_identifier column in our Reference table contains GI numbers and their presence is used to determine if the reference was originally dowloaded from the NCBI (and hance can be re-downloaded that way).

If we remove this column, we should add another column to contain the original source of the reference. This would have been a better option to start with I guess.