datasets to data sources

[josh-chamberlain]

Part of our official full-time work on PDAP has been making sure we're on the same page about terminology—one thing we are going to change is dataset → data source. I can't rename the DoltHub repo, so I cloned it and made a new one: https://www.dolthub.com/repositories/pdap/data_sources

This means a bunch of the stuff in pdap_dolt.py broke. We aren't going to be using dolt as our primary db for the foreseeable future, so it's probably going to be deprecated at some point soon anyway.

FWIW, I don't think we need to worry about all the data_intake and ETL stuff in here...this was my attempt at a find and replace to fix most of the issues.

[josh-chamberlain]

@thejqs want to do your first canonical PR approval?