title: Sonata Admin List Field Template is Ignored
body: <p>I'm using Symfony 4.1.1 and Sonata Admin Bundle 3.35.2.</p>
  
  <p>I want to use a custom template for a field in an admin's list view. The template is ignored. I am using Twig as my templating engine.</p>
  
  <p>In the admin:</p>
  
  <pre><code># /src/Admin/ImageAdmin.php
  
  protected function configureListFields(ListMapper $listMapper) {
      $listMapper
          -&gt;add('filename', 'string', ['template' =&gt; 'list_image.html.twig'])
      ;
  }
  </code></pre>
  
  <p>The template:</p>
  
  <pre><code># /templates/list_image.html.twig
  
  {% extends 'SonataAdminBundle:CRUD:base_list_field.html.twig' %}
  
  {% block field %}
      &lt;img src="{{ value }}" style="width: 200px" /&gt;
  {% endblock %}
  </code></pre>