code review & cleanup
Merge branch 'feature/merging' into develop
added list action to TagController
extracted load functions from TagController to TagManager
extracted delete action to TagManager
extracted merge action to TagManager
extracted save to TagManager
extracted updating a tag to TagManager
show a tag list in content editing
integrated TagList into Sulu
implemented storage of creator and changer
added users to tests
adjusted merge to handle multiple source tags
correcte TagManagerInterace PHPDoc
merged with feature/integragtion, implemented patch action
finished tests for patch action