background playback fix

Kai DeLorenzorequested to merge
background-playback-fix into master

fix https://www.reddit.com/r/grayjay/comments/1lfsz3r/twitchs_audio_only_mode_carries_over_to_other/ by forcing YouTube to play in video mode when on the limited version (prevent background carry over for YouTube)

make it so that switching to video works for all source types after launching a video with background playback carrying over

Changelog: changed

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