classes: webos_systemd.bbclass: add class for a common systemd recipe part for webos services

Signed-off-by: Simon Busch <morphis@gravedo.de>
audio-service: add initial recipe for the audio management service

Signed-off-by: Simon Busch <morphis@gravedo.de>
packagegroup-webos-ports-extended: add audio-service

Signed-off-by: Simon Busch <morphis@gravedo.de>