title: template name in twig main layout
body: <p>Is it possible in <strong>twig</strong> to get the name of the child template in the layout?
  For Example when calling:</p>
  
  <pre><code>$app['twig']-&gt;render('index.twig');
  </code></pre>
  
  <p>then in <em>layout.twig</em>, which is the main layout, it should ask:</p>
  
  <pre><code>if page is index.twig =&gt; include this javascript
  </code></pre>
  
  <p>I could do this with additional variables in the render call, but this seems to be bloated since the template name would indicate it already.</p>