Add an option to load a file containing redirects (source, target paths)
and serve them from the HTTP server, to allow renaming a radio without
breaking old links.

This provides some discovery capabilities to radiod and redirectord, so
that in most cases fewer command-line options are required for operation.

Also removed some unnecessary duplication of code from net/http.

Refactor the HTTP handler hierarchy to make it simpler.

Replace the ghost logging handler with a simpler one, that fires as soon
as the HTTP request headers are sent (this is a better solution for
long-lived connections).

Add a debug page to track long-lived HTTP request.

Add tests for the HTTP server.

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.