title: Get all eloquent models without relationship
body: <p>I would like to fetch all models that don't have a relationship.</p>
  
  <p>Similar to fetching models which have one:</p>
  
  <pre><code>return $this-&gt;model-&gt;has('quote')-&gt;orderBy('created_at', 'desc')-&gt;get();
  </code></pre>
  
  <p>I would basically like to have the inverse of this. I can't find any documentation to do this though.</p>
  
  <p>Basically this query:</p>
  
  <pre><code>SELECT * FROM custom_design_requests
  RIGHT JOIN quotes
  ON quotes.`custom_design_request_id` = `custom_design_requests`.id
  </code></pre>
  
  <p>But I'd like to avoid having to use the Query Builder (<code>DB::table('custom_design_requests')-&gt;rightJoin('quotes', 'quotes.custom_design_request_id', '=', 'custom_design_requests.id')-&gt;get();</code>), so that I have a collection of instances of the model.</p>
  
  <p>Thanks</p>