Refactor the load balancing code using a generic traffic control
abstraction that gives the user more control over the final logic (for
the moment this is configured via a command-line parameter).

Introduce node names, allowing a node to have multiple IP addresses.
Also, make the front-end code IPv6-aware and support AAAA records.

This allows running the service on a single port: with the
--enable-icecast-proxy option, all requests can go through
redirectord.