/**
  * Render the category index
  */
 public static function render($category_id, $partial)
 {
     $categories = Category::listAll();
     $content = '';
     if ($categories) {
         foreach ($categories as $category) {
             $postpartial = $partial;
             $postpartial = str_replace('{id}', $category->id, $postpartial);
             $postpartial = str_replace('{name}', $category->name, $postpartial);
             if ($category_id == $category->id) {
                 $postpartial = str_replace('{class}', 'current_page_item', $postpartial);
             } else {
                 $postpartial = str_replace('{class}', 'page_item', $postpartial);
             }
             $content .= $postpartial;
         }
     }
     return $content;
 }