Export the node Status as metrics.

Also add instrumentation for the load balancer module.

We only use the proxy for Icecast streaming so there's no need to be
generic.

Includes a merge of radiod and redirectord, updates to more modern Go
idioms, adoption of the higher level etcd concurrency primitives, and
a lot of other minor implementation changes.

The refactor is still incomplete: the daemons won't compile and the
code to start the RPC servers is missing.

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 change involves a refactoring of the DNS redirector code, which is
now a bit cleaner and has proper tests.

- Changed package name to autoradio-server to avoid conflicts;
- fixed systemd service files and defaults;
- added sudo configuration to restart icecast2;
- removed obsolete prerm/postrm scripts.

It should work with Debian wheezy (sysvinit) and jessie (systemd)
without having to pass a reload command as a command-line flag.