[DVDPlayer] Pre-filter subtitles streams to relevant ones before sorting them by priority.
[Settings/DVDPlayer] Add option "Prefer external subtitles" to category subtitles and adapt DVDPlayer accordingly.
[DVDPlayer] Prefer forced subtitles if "original stream's language" is set as subtitle preference.
[DVDPlayer] Change forced subtitle when changing audio track.
[DVDPlayer] Add a doxygen comment to the class PredicateSubtitleFilter.
[DVDPlayer] Add a doxygen comment to the class PredicateSubtitlePriority.
[OMXPlayer] Pre-filter subtitles streams to relevant ones before sorting them by priority.
[OMXPlayer] Add option "Prefer external subtitles" to category subtitles and adapt DVDPlayer accordingly.
[OMXPlayer] Prefer forced subtitles if "original stream's language" is set as subtitle preference.
[OMXPlayer] Change forced subtitle when changing audio track.
[OMXPlayer] Add a doxygen comment to the class PredicateSubtitleFilter.
[OMXPlayer] Add a doxygen comment to the class PredicateSubtitlePriority
Merge pull request #3396 from ace20022/default_sub_sel

[DVDPlayer] Improve preferred subtitle selection