title: Rails Admin custom column for association table
body: <p>I am using Ruby 2.3, Rails 4.2.7 &amp; rails-admin 1.2.0</p>
  
  <p>I have an issue with the association column for showing in the List.</p>
  
  <pre><code>Class Address &lt; ActiveRecord::Base
    belongs_to :user
  
    # Have to write custom because Rails Admin doesn't allow to add multiple columns from the association table.
    def custom_column
      self.user.email
    end
  
    rails_admin do
      list do
        include_fields # it only works on the current model
        field :id
        field :custom_column
        field :user
        field :address
      end
    end
  end
  </code></pre>
  
  <p>The custom column always positioned in the last. Is there any way to put the column in any position ? The custom column is of User Model.</p>