Duplicate form elements
As an editor I want to duplicate a form element in form editor. This should be possible for all elements.
When duplicating a container element (e.g. grid row and fieldset), all sub elements will be also duplicated.
There should be a new button (or new context menu) on the form element on stage to duplicate en element quickly by just one click.
The copy is technically (YAML) completely the same except for the identifier.