Add DOI to the DB

[micahjohnson150]

Its come up a couple times on how to distinguish datasets that are published to the NSIDC that are in the DB and those that are still in progress. I think we should add a DOI column for all data. If that the column is None then this is an anticipated dateset. If it has one, then we know it came from the NSIDC. @meganmason and I came up with the idea of having a script to update a list of datasets anticipated/published in the repo for hackweek users to reference which I think would be very useful for project sessions.