Add support for WIDEVINE encrypted DASH streams

[goggle]

Closes https://github.com/goggle/plugin.video.rtsplaytv/issues/10

[goggle]

TODO:

• Extract all audio tracks (currently only the English track is extracted)
• Does not work: https://www.srf.ch/play/tv/station-19/video/prioritaeten-staffel-4-folge-10?urn=urn:srf:video:fcc1fed3-ea7e-48c1-b9bd-8e9032aca06d

Edit: listitem.setProperty('inputstream.adaptive.original_audio_language', 'fr') does not seem to have an effect. But the audio tracks do get extracted, so the user can toggle the audio stream in the settings.