[release] version bump to 13.1 rc1
Merge pull request #4742 from MartijnKaijser/13.1rc1

13.1rc1
[lang] update of internal addon language files
[lang] update of core language files
[lang] update of skin.confluence language files
Merge remote-tracking branch 'xbmc-original/Gotham' into 13.1-Gotham-pivos