edit question: textNode no answerDomain/required element needed
fixes: questionnaire_id & parent_id moved from question-subform to main form
fixes setting of questionnaire_id is one niveau deeper, because of many-one relationship
remove form-decorator from 'subform'
Tests for edit/add question subform: isValid function
adjustments to form add/edit likert table

* generate question rows (subform questions) in seperate form
QuestionsRows
* data.yml: LikertElement has also answerDomainChoice (so have the
questions)
* properties/LikertNode: LikertNode has no required for complete group
(questions have)
* models QuestionnaireGroupNode: hack: descendants has no relation by
default
* questionnaire-question.js: make questions-rows-sortable as well