The purpose of this operation is to separate the serving of GUI assets a
bit from the serving of the REST API. It's by no means complete. The end
goal is something like a combined server type that embeds a statics
server and an API server and wraps it in authentication and HTTPS and
stuff, plus possibly a named pipe server that only provides the API and
does not wrap in the same authentication etc.
GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3273
