title: Active Admin: pass instance variable for custom page
body: <p>I have a custom page in ActiveAdmin called statistics, where I want to display charts with data from the database.</p>
  
  <p>Now I used the <a href="http://railscasts.com/episodes/324-passing-data-to-javascript?view=asciicast" rel="nofollow">Gon gem</a> and want to pass the data to my custom page through an instance variable.</p>
  
  <p>Usually you would add the gon line to the index action</p>
  
  <pre><code>class ProductsController &lt; ApplicationController
    def index
      gon.rabl "app/views/products/index.json.rabl", as: "products"
    end
  end
  </code></pre>
  
  <p>But there is no controller in active admin for my custom page. How should I do this?
  Or do I have to do this through the dashboard?</p>