This commit adds a shutdown logger which will send a request for
shutdown on critical errors. It uses the signal package to request safe
shutdown of the daemon. Since we init our logs in config validation,
we add a started channel to the signal package to prevent the case where
we have a critical log after the ShutdownLogger has started but before
the daemon has started listening for intercepts. In this case, we just
ignore the shutdown request.
If the main package is used as a library, we don't want it to
register interrupt signals itself. Rather we want to pass in the
shutdown channel manually. We do this in the cmd now.
ListenerCfg allows passing custom listeners to the main method, to be
used for the wallet unlocker and rpc server. If these are set these will
be used instead of the regular RPC listeners.
