We need to set these properties *before* Angular starts making requests,
and doing that from the response to a request is too late. The obvious
choice (to me) would be to use the angular $cookies service, but that
service isn't available until after initialization so we can't use it.
Instead, add a special file that is loaded by index.html and includes
the info we need before the JS app even starts running.
GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3152
