Backfill

[cjcobb23]

We should look into adding functionality for clio to backfill data. Right now, Clio only moves forward in time, so if you have an existing database, there's no way to get older data without just wiping the database and starting over. There still should be no history gaps. I think it should be straightforward to apply diffs in reverse, though things might get complicated with the successor table being developed as part of caching.