Fix scaffolding multivalued complex properties in Designer

In Studio Modeler

• Create a schema with a complex multivalued property e.g. toto
• Add two subwidgets to it of type string and date (multivalued), e.g. totomultistring and totomultidate

In Studio Designer

• Scaffold the edit layout for the toto document type
• Drag and drop the toto property in edit mode into the layout
• Edit the nuxeo data table element that has been created for it
  => Six colums appear instead of 2