[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 branch 'Gotham' of https://github.com/xbmc/xbmc into Gotham