title: How to add an HTML-class to an ActiveAdmin index table
body: <p>For some custom (ordering) Javascript, I'd like to add a class, "sortable" to the table in an <code>ActiveAdmin</code>-resource.</p>
  
  <p>The default generated HTML is:</p>
  
  <pre><code>&lt;table cellspacing="0" cellpadding="0" border="0" paginator="true" class="index_table index" id="products"&gt;
  </code></pre>
  
  <p>I'd like to add a class:</p>
  
  <pre><code>&lt;table ... class="index_table index sortable" ...&gt;
  </code></pre>
  
  <p>Or, if that is not possible, a "data-sortable" property. Like so:</p>
  
  <pre><code>&lt;table ... data-sortable="products"&gt;
  </code></pre>
  
  <p>I've tried to pass in some HTML-ish hashes, but they are not picked up:</p>
  
  <pre><code>index(:class =&gt; "sortable") do
  end
  
  index(:html_attributes =&gt; {:class =&gt; "sortable"}) do
  end
  </code></pre>
  
  <p>Reading the <a href="http://rubydoc.info/gems/activeadmin/ActiveAdmin/Views/IndexAsTable%3abuild" rel="nofollow">documentation</a> makes me no wiser. </p>
  
  <p>How can I add custom classes or attributes to the table?</p>