title: wp_list_categories - add class to list items
body: <p>I am trying to style my wordpress category listing to add a class of <code>list-group-item</code> to each li element as follows:</p>
  
  <pre><code>&lt;ul class="list-group"&gt;
      &lt;li class="list-group-item cat-item cat-item-12"&gt;&lt;a href="..." title="View all posts filed under ..."&gt;...&lt;/a&gt;&lt;/li&gt;
      &lt;li class="list-group-item cat-item-14"&gt;&lt;a href="..." title="View all posts filed under ..."&gt;...&lt;/a&gt;&lt;/li&gt;
  &lt;/ul&gt;
  </code></pre>
  
  <p>Extending the <strong>WP_Widget_Categories</strong> Class</p>
  
  <pre><code>Class GdCategoriesWidget extends WP_Widget_Categories {
  
  function widget( $args, $instance ) {
  
          // Most of widget method deleted out for S/O readability.
  
      ?&gt;
      &lt;ul class="list-group"&gt;
  &lt;?php
      $cat_args['title_li'] = '';
  
      wp_list_categories( apply_filters( 'widget_categories_args', $cat_args ) );
  ?&gt;
          &lt;/ul&gt;
  
      // After Widget stuff deleted out for S/O readability
  
  }
  </code></pre>
  
  <p>De-registering original and registering my custom widget</p>
  
  <pre><code>function gd_widget_registration() {
      unregister_widget('WP_Widget_Categories');
      register_widget('GdCategoriesWidget');
  }
  add_action('widgets_init', 'gd_widget_registration');
  </code></pre>
  
  <p>The problem that I am facing is that I cannot see anywhere in the docs <a href="http://codex.wordpress.org/Template_Tags/wp_list_categories#Markup_and_Styling_of_Category_Lists" rel="nofollow">http://codex.wordpress.org/Template_Tags/wp_list_categories#Markup_and_Styling_of_Category_Lists</a> where I can override the class applied to list items.</p>