title: ActiveAdmin actions
body: <p>is there a way to specify in ActiveAdmin's index page of a model what actions are allowed, things like:</p>
  
  <pre><code>index do
    actions :edit
  end
  
  index do
    actions only: :edit
  end
  </code></pre>
  
  <p>do not work. What's the correct syntax?</p>
  
  <p>Appreciated.</p>
  
  <pre><code>bundle show activeadmin
  /home/muichkine/.rvm/gems/ruby-2.1.2/bundler/gems/active_admin-9cfc45330e5a
  </code></pre>