Update the mass creation form, so that you can see the newly created entities in dropdown

Fixes issue #1103

src/Controller/AdminPages/BaseAdminController.php

@@ -383,6 +383,9 @@ abstract class BaseAdminController extends AbstractController
             if (count($results) > 0) {
                 $this->addFlash('success', t('entity.mass_creation_flash', ['%COUNT%' => $created_count]));
             }
+
+            //Recreate mass creation form, so we get the updated parent list and empty lines
+            $mass_creation_form = $this->createForm(MassCreationForm::class, ['entity_class' => $this->entity_class]);
         }
 
         return $this->render($this->twig_template, [