subs: move rendering to text subtitles to overlay renderer

This fixes issues with 3d modes where subtitles would apear on
one eye before the other, due to timestamps differing between
render passes.
settings: add CSetting::Clone()
CSettingAddon/Path: implement Clone()
settings: add CSettingList implementation
settings: add GetList()/SetList() to CSettingsManager
settings: add wrapper for GetList()/SetList() to CSettings
settings: add multiselect support to list control
[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 #3565 from elupus/subsgui

subs: move rendering to text subtitles to overlay renderer