Fix: [Emscripten] switch to URL for content-service that supports WebSocket (#11106)

In the old days, content.openttd.org and bananas-server.openttd.org
ended up on the same route. But with a recent migration, they do not.
content.openttd.org only serves the custom TCP protocol, and
bananas-server.openttd.org only serves the HTTP(S).

Websockets use HTTPS, and as such, should be routed via the latter.

Change: use TCP for everything except for master-server and initial server scan (#9130)

This means that pressing Refresh button and adding servers manually
now uses TCP.

The master-server and initial scan are still UDP as they will be
replaced by Game Coordinator; no need to change this now.

If we query a server that is too old, show a proper warning to the
user informing him the server is too old.

Add: support for emscripten (play-OpenTTD-in-the-browser)

Emscripten compiles to WASM, which can be loaded via
HTML / JavaScript. This allows you to play OpenTTD inside a
browser.

Co-authored-by: milek7 <me@milek7.pl>