Get the downloadable EEPROM lists of every known cape vendor

Fetches the vendor index from fpp-data and then each vendor's own list, all server-side, so the browser makes one same-origin request. Doing this from the browser needed every vendor host in the CSP connect-src AND sending CORS headers, and most vendor hosts do neither (issue seen with a vendor list hosted on the bare domain while the CSP carried the www. form). The eeprom file itself was already downloaded server-side by upgradeCapeFirmware.