title: Using Bootstrap 3 form theme in symfony2 does nothing
body: <p>I'm trying to use Bootstrap3 form theme in my Symfony2 forms as described here:<br>
  <a href="http://symfony.com/blog/new-in-symfony-2-6-bootstrap-form-theme" rel="nofollow">http://symfony.com/blog/new-in-symfony-2-6-bootstrap-form-theme</a></p>
  
  <p>I'm adding this in main config:  </p>
  
  <pre><code>twig:
      form:
          resources: ['bootstrap_3_layout.html.twig']
  </code></pre>
  
  <p>And adding this in every form:  </p>
  
  <pre><code>{% form_theme form 'bootstrap_3_layout.html.twig' %}
  </code></pre>
  
  <p>classes are applied to html elements but no theme is applied.<br>
  I checked page source and found no bootstrap.css (Should I include it by myself? )<br>
  I included bootsrap but still I had a very bad and messy full width textboxes and nothing else got affected!
  My symfony is <code>2.6.4</code> (upgraded from <code>2.5.10</code>)<br>
  What is the problem?</p>