Enable GUI setting for CEC adapter to stop/pause media playback on TV Standby action

[mlansky]

Useful to free TVHeadend TV adapter for other Kodi clients.

Needs only very small change to peripherals.xml

CEC Options missing in settings menu

I run TVHeadend TV server on my Pi3 with latest OSMC. The Pi3 is connected to TV and AMP via HDMI. I use the Pi3 as well as several other Kodi clients in my house to watch TV. When I put the TV on Standby, I would like to stop media playback on the Pi3 to free the TVHeadend DVB-S adapter for other clients. However, in the Kodi Settings/System/Device/CEC-Adapter menu, I can only choose “Ignore” “Standby” or “Switch off” as option during CEC TV Standby event. The menu settings “Pause Playback…