Dashboard cleanup

[mnlevy1981]

The dashboard doesn't work on glade systems because the absolute path to png_catalog.csv is set as f"{path}png_catalog.csv" and path does not contain a trailing / for glade. We should use os.path.join() for file paths and f"{path}/png_catalog.csv" for URLs (we don't want Windows users to try to find https://webext.cgd.ucar.edu/g.e22.G1850ECO_JRA_HR.TL319_t13.004\png_catalog.csv)