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
Minor Posts fixes

* Whitespace fixes
* Fix handling of form_id in posts api: no PHP error if missing
* Only check parent exists if not empty
Merge branch 'master' into posts-updates