added language-chooser and href-lang tags
updated upgrade md
added twig helper to generate meta tags
Merge pull request #374 from sulu-cmf/feature/language-chooser

Added language-chooser and href-lang tags
updated translation files for admin
Merge branch 'develop' of github.com:sulu-cmf/sulu-standard into develop
updated translation files for admin
Updated for https://github.com/sulu-cmf/sulu/pull/524