Add support for additional types of subtitles

Note to add support for more types of subtitles, embedded and external subtitles including SubRip (.srt), WebVTT (.vtt), Timed Text (.ttxt), YouTube (.xml), SubStationAlpha (.ass), DVB Teletext, Closed captions etc

Done in today’s 2.6.2 beta build. MCEBuddy can process all types of text subtitles/closed captions/teletext and convert them to substip (srt).