Improve reverse proxy support

Should address edge cases and close #224 -- subject to field testing.

Does require the NGINX deployments use the following:

proxy_pass <http://documize-url:5001>;
proxy_set_header Host $http_host;
proxy_set_header X-Forwarded-For $remote_addr;

vendor/github.com/gorilla/handlers/handlers_pre18.go

@@ -0,0 +1,7 @@
+// +build !go1.8
+
+package handlers
+
+type loggingResponseWriter interface {
+	commonLoggingResponseWriter
+}