title: Activeadmin has_many form for show and edit only
body: <p>First please note that i am working with rails 4 and activeadmin rails 4 branch. <a href="https://github.com/gregbell/active_admin/tree/rails4" rel="nofollow noreferrer">https://github.com/gregbell/active_admin/tree/rails4</a></p>
  
  <p>I have two models pictue which is ploymorphic</p>
  
  <pre class="lang-rb prettyprint-override"><code>class Picture &lt; ActiveRecord::Base
   belongs_to :picture_category
   belongs_to :imageable, polymorphic: true
  
   mount_uploader :image, ImageUploader
  end
  </code></pre>
  
  <p>And ship</p>
  
  <pre class="lang-rb prettyprint-override"><code>class Ship &lt; ActiveRecord::Base
    has_many :pictures, as: :imageable
    accepts_nested_attributes_for :pictures
  end
  </code></pre>
  
  <p>And activeadmin ship.rb</p>
  
  <pre class="lang-rb prettyprint-override"><code>ActiveAdmin.register Ship do
  
     form do |f|
        f.inputs do
        f.inputs
          f.has_many :pictures, :sortable =&gt; :picture_categories do |ff|
            ff.input :name
          end
        end
     f.actions
     end
  
   controller do
     def permitted_params
       params.permit(:ship =&gt; [:name, :title, :short_desc, :description, :position, :pictures, :enabled, :ship_provider_id, :picture_category_id, :picture_id])
     end
   end
  end
  </code></pre>
  
  <p>but the result is this:</p>
  
  <p><img src="https://i.stack.imgur.com/xZGJ3.png" alt="enter image description here"></p>
  
  <ol>
  <li>How can get rid of delete button and have submit</li>
  <li>how can i show this form only on show and edit form because thats not make sense having child before parents</li>
  </ol>
  
  <p>Please point what are mistakes in code.</p>