Minor fixes to groups and attributes

* Remove attribute data from groups test posts
* Change test group labels - for more sanity and reuse in docs
* Add test to check all attribute values are saved in POST attributes
* Add test to check all attribute values are saved
  in POST forms/:form_id/groups/:group_id/attribute
* Add test to check all attribute values are saved in POST /forms
* Fix forms, attributes, and group attributes API calls to save all values