feat: rendering of forms and sub-forms

discuss whether the formNode property is required in a NodeShape to decide if a form may be rendered or not; dash proposes the use of a DetailsEditor for the corresponding PropertyShape

If a PropertyShape P exists, that has a NodeShape N as its sh:node property, N is a NodeShape that is (also) used as a nested Form.

--> this offers nothing to decide wether N should be selectable as a root node/top level shape.

This is relevant, because only top level NodeShapes would get or create accessible IDs while lower level NodeShapes would be inserted as blank nodes.