Reverse proxy wrapper now supports configuration of the http headers to utilize for determining prefix and scheme

Introduced two new configuration settings, server.reverseProxy.prefixHeader and server.reverseProxy.schemeHeader to define the headers to evaluate for prefix and scheme to use respectively, also moved server.baseUrl and server.scheme to server.reverseProxy.fallbackPrefix and server.reverseProxy.fallbackScheme.

Also fixed SockJS URI as generated in index.jinja to include BASE_URL.

 Should do what PR #507 intended, but with less code duplication.