re-enables shortwave radiation data downloads and adds new IEM data download links. Also retroactively adds a release note for the release that closed the radiation downloads.
renames the links to the new data download links from last commit: https://github.com/ua-snap/snap-www/commit/125afc9afef82299a29b245e4335d51777857769
 -they had a certain tag removed from their filenames between then and now.