Mark newly created entities better in structural entity selector

src/Form/Type/Helper/StructuralEntityChoiceHelper.php

@@ -86,6 +86,9 @@ class StructuralEntityChoiceHelper
             $tmp += ['data-filetype_filter' => $choice->getFiletypeFilter()];
         }
 
+        //Show entities that are not added to DB yet separately from other entities
+        $tmp['data-not_in_db_yet'] = $choice->getID() === null;
+
         return $tmp;
     }