Restore user captions settings

[snoesberger]

As with the playback rate, volume, etc., it would be nice to be able to save the subtitle settings that the user has chosen. For example, if a user activates Spanish subtitles for the video they are watching, the next time they open a video, the Spanish subtitles, if available, will be displayed automatically.

Again, like for the playback rate and volume, the behaviour should be configurable in the config.json:

"videoContainer": {
        "restorePlaybackRate": true,
        "restoreVolume": true,
...