[LanguageSystem] WIP: Added language entry classes
[LanguageSystem] WIP: Uses versionID now

* Added foreign keys
* Replaced contentID with contentVersionID (basically versionID)
[LanguageSystem] WIP: Fixed file ending
[LanguageSystem] WIP: Added cache classes
[LanguageSystem] WIP: Removed usage of {lang}

* {lang} isn't used anymore for the dynamic contents
* that is only valid for Contents as of now
[LanguageSystem] WIP: Implemented I18n cheating

* The Content*Form controllers use the new language system now
* and thereby cheat on I18nHandler
[LanguageSystem] WIP: Updated updateSearchIndex

* The method updateSearchIndex uses now new language system
[LangSystem] WIP: Updated save, updateSearchIndex

* Updated save method with new language system
* Fixed updateSearchIndex (replaced contentID with versionID)
[LangSystem] Categories use new lang system now
[LangSystem] Fixed cache reset
[LangSystem] Added missing class description
[LangSystem] Pages use now new lang system
[LangSystem] Fixed typo
[LangSystem] Removed removal of lang vars
Merge branch 'feature/235' into dev