allows to check if an obj_class or attribute already exists in the CMS

+ the caller can handle what should happen, if it does not exist by rescue from DuplicateResourceError
+ adopts existing generators (kickstart, attribute, google_analytics and model)
updates google analytics to use variables set in the generator
bugfix: used wrong homepage path

+ refactored paths into variables
Merge branch 'feature/check-structure-exists' into develop

* feature/check-structure-exists:
  bugfix: used wrong homepage path
  updates google analytics to use variables set in the generator
  allows to check if an obj_class or attribute already exists in the CMS