CUtf8Utils: add "checkStrForUtf8()"
New UTF-8 string check, based on current Unicode standard (6.3), with three result values: plain ASCII, valid UTF-8, high ACSII.
fixed: We can't grab the duration from the streamdetails for stacks
Utf8Utils: add "isValidUtf8()" for convenient check for valid UTF-8 strings
Remove usage of CharsetConverter.isValidUtf8()
CharsetConverter: remove outdated "isValidUtf8()"
mpegts: do not set pts for missing dts in video streams

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
ffmpeg: add patch for backport: mpegts-do-not-set-pts-for-missing-dts
[subtitles] check and get idx/sub pair when download.
[coreSubs] proper fix for cf85bdb , select services list if no subtitles are found
VideoInfoScanner::EnumerateEpisodeItem: don't use ToLower with UTF-8 strings, fixes #14728
Not needed as RegExps are done in caseless mode
[lang] update of internal addon language files
[lang] update of core language files
[lang] update of skin.confluence language files