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Showtime: enable YouTube-style keyboard controls

Use similar controls as on YouTube when watching Showtime (`f` for full screen, `k` to play/pause, `c` for captions, `m` to mute/unmute, `p` to enable/disable PiP, `j`/`l` to go back/skip 10 seconds, left/right arrows for 5 seconds, `0`..`9` for 0% .. 90%)