Make script Kodi 18 compatible.

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Kodi 18 API removed onPlayBackStarted from xbmc.Player() and uses onAVStarted() instead.

Please note: This PR will stop the script being compatible with Kodi 17 due to the function change. This is a Kodi 18 ONLY PR

https://codedocs.xyz/AlwinEsch/kodi/class_c_application.html#ac7bb3dfcbbd434a485644ae7c4084af8

Function: onPlayBackStarted()

onPlayBackStarted method.

Will be called when Kodi player starts. Video or audio might not be available at this point.

v18 Python API changes: Use onAVStarted() instead if you need to detect if Kodi is actually playing a media file (i.e, if a stream is available)

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Seeing as this script is not in development by the dev the PR will not get merged. It is better for me to close it and link to the forked Kodi 18 version

https://github.com/lorkadiscovery/script.kodi.hue.ambilight