title: Activeadmin: destroy / add has_many relations content
body: <p>I have this 2 models (echanges and echange_answers) in a relation: </p>
  
  <blockquote>
    <p>has_many 
    / 
    belongs_to</p>
  </blockquote>
  
  <pre><code>#Model Echange
  class Echange &lt; ActiveRecord::Base
    attr_accessible :content, :title
    validates_presence_of :title, :content, :section_id
    validates :section_id, numericality: { only_integer: true }
    validates :title, length: { :minimum =&gt; 3 }
    validates :content, length: { :minimum =&gt; 3 }
  
    belongs_to :section
    belongs_to :user
    has_many :echange_answers
  end
  </code></pre>
  
  <p>and</p>
  
  <pre><code>#Model EchangeAnswer
  class EchangeAnswer &lt; ActiveRecord::Base
    attr_accessible :content
  
    validates_presence_of :content
    validates :content, length: { :minimum =&gt; 3 }
  
    belongs_to :user
    belongs_to :echange
  end
  </code></pre>
  
  <p>And here is what i got in active admin :
  A list of all the "echanges" made</p>
  
  <p><img src="https://i.stack.imgur.com/UneOE.png" alt="List of echanges"></p>
  
  <p>And here is the show of one of the echange. I print on the page all the echange_answer that are in a belongs_to relation with this echange.
  <img src="https://i.stack.imgur.com/7delU.png" alt="Show page of a echange"></p>
  
  <p>I would like to set a delete / edit action on each echange_answer in that table and the possibility for the admin to add a new echange_answer.
  I am wondering if the best way is not to create a new active_admin:resource and remove the "index" page or to custom the echange page in activeadmin.
  If the custom is the best way, how could i do it ?</p>