properly send `User-Agent` and `Accept-Language` to `updateJson` server, module developers can check `User-Agent` whether to send update to user and set user preferred language for changelog. also added cache to reduce update server load
properly send `User-Agent` and `Accept-Language` to `updateJson` server, module developers can check `User-Agent` whether to send update to user and set user preferred language for changelog. also added cache to reduce update server load