title: How to override default_scope in ActiveAdmin in Rails
body: <p>In a resource registered with ActiveAdmin, I have the following default_scope defined for the model:</p>
  
  <pre><code>default_scope :order =&gt; 'activities.updated_at DESC'
  </code></pre>
  
  <p>This apparently prevents me from being able to change the sorting on the resource's index page by clicking on the column titles.  Is there a way to keep this default scope but get Active Admin sorting to work?</p>