title: Sort a table_for in rails activeadmin
body: <p>In an active admin show page, I've got two panels, the first being the primary record, the second being associated info (by has_many) so <code>show</code> looks like this:</p>
  
  <pre><code>panel "Max Amount" do
    table_for user.max_amount do
      column 'Amount', :amount
      column 'time', :updated_at
    end
  end
  </code></pre>
  
  <p>Can i sort this high-to-low (or low-to-high) on the amount column?</p>
  
  <p>Update: I found the source for the demo ( <a href="https://github.com/gregbell/demo.activeadmin.info/blob/master/app/admin/users.rb">https://github.com/gregbell/demo.activeadmin.info/blob/master/app/admin/users.rb</a> ) which seems to have sorting but when you go to the actual demo site it's not working. Is this feature perhaps broken? Is there a work-around?</p>