Universal Port: Simplified administration for rippled servers

This implements part of the "Universal Port" feature. It allows peer, RPC over http, RPC over HTTPS, Websocket, and Secure Websockets to be served on a single listening port. In this version, websockets is disabled and only legacy peer connections are allowed to become peers. Peer HTTP upgrade requests are given a "503 Service Unavailable" with a JSON content body with a handful of IP addresses to visit.
Reviewers: @ximinez, @JoelKatz 
It's not a significant number its just a default used for outgoing. And I think 6561 is quite out of date. We should probably change it to 51235. Or better yet, return an error if they leave the port unspecified.