Update Solar Resource downloads for latest NSRDB datasets

[cpaulgilman]

Review https://developer.nrel.gov/docs/solar/nsrdb/ to be sure Solar Data Download UI callback script is accessing latest data, including new polar datasets, https://developer.nrel.gov/docs/solar/nsrdb/nsrdb-polar-tmy-v4-0-0-download/

Note that all NSRDB datasets should be available using the Advanced download option in SAM.

Also, NSRDB Viewer always provides access to the latest datasets: https://nsrdb.nrel.gov/data-viewer