Backend changes for CSV export, updates to data loader, new data

This PR includes:

- backend updates to add in the CSV export
- updated url for the csv download (`/api/rates/csv/?`)
- updated url in the template for csv download
- updates to the data loader to accommodate new data
- the actual new data from Kelly

@shawnbot can you update the JS to not pass in the `format=csv` query parameter to the export link? It works, it's just superfluous. I ended up making the CSV export its own view that doesn't inherit from `APIView` because it was a lot easier. I just abstracted the shared logic into its own function instead.