Language selection seems to break BASE_HREF

[jneubert]

When selecting another interface language (in the upper right corner), the URL changes. Instead of the reverse proxy path (as described in #352) the IP address behind the proxy becomes part of the URL, with consecutive CORS issues while accessing css and font resources.

[osma]

Yes, the code for creating the links (in view/topbar.twig) seems to rely on request.requesturi so it is affected by the server environment.