title: How to get entity or pass variable to Symfony2 twig form widget?
body: <p>In my <em>edit.html.twig</em> I have:</p>
  
  <pre><code>{% form_theme edit_form 'MyBundle:Entity:form.html.twig' %}
  {% set img_src = asset('120x100.jpg') %}
  {{ dump(img_src) }}
  {{ dump(entity) }}
  {{ form_widget(edit_form, {'form_type': 'horizontal', 'img_src': img_src }) }}
  </code></pre>
  
  <p>There I have <strong>img_src</strong> and <strong>entity</strong> dumped with no problem.<br>
  In <em>form.html.twig</em> I have:</p>
  
  <pre><code>{% extends 'MyBundle:Form:bootstrap.html.twig' %}
  {% block _entity_field_widget %}
      {{ dump(img_src) }}
      {{ dump(entity) }}
      {% set type = 'hidden' %}
      {{ block('form_widget_simple') }}
  {% endblock _channel_media_widget %}
  </code></pre>
  
  <p><em>bootstrap.html.twig</em> is just a bootstraped *form_div_layout.html.twig*<br>
  And in that widget I have no <strong>img_src</strong> nor <strong>entity</strong>.<br>
  Any ideas how to get entity in widget? Should it be passed to form widget or is there another way? What am I doing wrong?</p>