Add two new headers to proxy.conf

Fixes #1609. Adding both  X-Forwarded-Host  and X-Forwarded-Port, this is vital for some services behind a proxy (used to allow creation of absolute links in html). I've had to include at least the Host version in the past for jenkins and nexus.
Been running locally for 24 hours, does not appear to break any of my 15+ services currently running behind NPM would allow people to host those services without the need for advanced configuration

docker/rootfs/etc/nginx/conf.d/include/proxy.conf

@@ -2,6 +2,8 @@ add_header       X-Served-By $host;
 proxy_set_header Host $host;
 proxy_set_header X-Forwarded-Scheme $scheme;
 proxy_set_header X-Forwarded-Proto  $scheme;
+proxy_set_header X-Forwarded-Host   $host;
+proxy_set_header X-Forwarded-Port   $port;
 proxy_set_header X-Forwarded-For    $remote_addr;
 proxy_set_header X-Real-IP          $remote_addr;
 proxy_pass       $forward_scheme://$server:$port$request_uri;