Edit question: improved validation/setDefaults/ and more

* QuestionnaireNode/Properties: improve isValid: (partial)validate all
forms, moved setDefaults to Properties/QuestionNode.php
* QuestionnaireNode/Properties/QuestionNode.php: setDefaults, if new
answerDomain choosen (now or earlier)
* questionnaireQuestionControler: renamed questionnaireQuestion to
questionnaireNode
* questionnaireQuestionControler: adjusted actOnSituation (but should be
moved to model)