mixer: sleep: Add --initial-mood and --initial-delay.

mixer: sleep: Add --initial-mood and --initial-delay.

The new options allow the user to run the sleep subcommand to do the
equivalent of

	$ para_client stop
	$ # set initial volume
	$ para_client select m/initial
	$ para_client play
	$ sleep $initial_delay
	$ para_mixer sleep

Fortunately, the implementation is very simple.