Add Access-Control-Allow-Origin to remote-access responses

[m10653]

Adds Access-Control-Allow-Origin: * to all responses served by the
remote-access HTTP server, so cross-origin browser pages can read from
the API.

Motivation

Lack of CORS headers makes it hard to build standalone dashboards, bookmarklets,websites, or static
HTML tools that talk to a Phyphox phone app even when the user is on the same local network.

I'm aware this PR may not be accepted as relaxing CORS on the server does have some security implications.

[Staacks]

Thanks, makes perfect sense. In fact, I just discussed a use-case two days ago where CORS could be a headache.

I plan to merge our current development branches over the next days to finally work on a beta for the next release and I will include this PR.