relocated ContentNavigation
extracted ContentNavigationItem from NavigationItem
changed content navigation representation
fixed tests according to new content navigation
adjusted to new ContentNavigationItem structure
started correct aura component
added new testcase
added some code documentation
cleaned some code and inserted persistend sulu header dom elements
Merge branch 'develop' into feature/content-navigation-refactoring

Conflicts:
	Resources/public/js/aura_extensions/sulu-content.js
cleaned code
Merge pull request #149 from sulu-cmf/feature/content-navigation-refactoring

[FEATURE] Introduce content navigation groups