refactored login and logout

- introduced session service
- service now uses restangular instead of $http
removed active view parameter from navigationcontroller because this can be handled by ui-router mechanisms
replaced navigation methods with ui-router's ui-sref directive
formatted navigation.html
navigation controller refactoring

- refactored states name hierarchy
- used multiple named views
navigation controller refactoring

- introduced navigation item directive
navigation controller refactoring

- introduced navigation item directive
navigation controller refactoring

- introduced navigation item directive
navigation controller refactoring

- fixed broken navigation links in ui-router
- changed navigation links form absolute to relative in ui-router
- fixed wrong navbar width in chrome