Added so webui cares about HTTP_X_FORWARDED_PROTO header

With this patch the webui module will care about the HTTP_X_FORWARDED_PROTO header. This is very useful if the webui for some reason is behind a proxy that is doing SSL offload. Without this patch all pages was redirected back to http:// instead of https://.

I am running Shinken webui behind a nginx proxy using SSL and that works fine.