Change Audio Module to explicit enable

[fel115]

#75 (comment):
Somehow like this:

if audio/bell != /dev/null || audio/alarm != /dev/null {
	let audio_bell = config.get::<String>("audio/bell");
	let audio_alarm = config.get::<String>("audio/alarm");
	tasks.push(spawn(Audio::get_background_task(
		Audio::new(audio_bell, audio_alarm),
		audio_receiver,
		nextcloud_sender.clone(),
	)));
}

Or add a audio_enable to the elektra config.