Fix Table Editor not saving layout when it contains an import

Steps to reproduce:

• In Modeler:
  • Create a PageProvider (pp).
• In Designer:
  • Create a Layout Block (layout-block).
  • Configure the results layout for pp.
  • Edit the table and switch to the table editor.
  • Drag and drop the dc:description field inside the table and save.
  • Refresh the page. Edit the table and switch to the table editor => dc:description should still be there.
  • Remove dc:description and save.
  • Switch to results editor and switch to code.
  • On the top of the file add an import to the layout block created previously:

    <link rel="import" href="../../forms/layout-block.html">
    

  • Save. Switch to view, then edit the table and switch to the table editor.
  • Drag and drop the dc:description field inside the table and save.
  • Refresh the page. Edit the table and switch to the table editor => dc:description is no longer there because the save action did not persist the changes.