Fix <input-many> and  <sortable-input-many>

  1. In `<input-many>`, after pressing the +Add button, "for=" attribute of the field `<label>`s for newly created inputs are not updated, and they are still pointing the hidden template.

  2. In `<sortable-input-many>`, after dragging/moving a item, "id="s and "name="s are still unchanged.

  3. In `<sortable-input-many>`, after dragging/moving a item, visibility of +/- buttons are not updated.

The integration test app doesn't cover these issues, but you can reproduce them manually on /projects/:id/edit.