Improve output download service

[nwagenbrenner]

It's possible for the app to get into a state where the app thinks the download completed normally when it actually didn't. For example, this just happened when I was downloading on 4G and switched to WiFi during the download. WindNinja thought the download completed normally, but when I try to view the results, the legend shows up, but the vectors do not plot. Ideally, the app would know that the download was not successful and would automatically retry. It could also be good to have an option to manually force a re-download of the results.