WebApp: (Low priority) Maybe replace xmlhttprequest with the Fetch API?

[viktorsmari]

We are using xmlhttprequest to talk to our kit API:
https://github.com/fablabbcn/smartcitizen-kit-20/blob/master/esp/data/main.js#L110-L128

Maybe there are some benefits of using the also built-in Fetch API instead of xmlHttp?

See pros vs cons here:
https://stackoverflow.com/questions/35549547/what-is-the-difference-between-the-fetch-api-and-xmlhttprequest