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: @nbougalis, @miguelportilla