title: Send email from WooCommerce when order status is changed to a custom order status
body: <p>I have created a custom order status in my WooCommerce installation, called Quote.</p>
  
  <pre><code>/* 
  * Change order status on new orders depending on order contents:
  *  If any product in the order is availble for quote, return 'quote' status. 
  *  Otherwise the order status will be set to processing.
  */
  add_filter ('woocommerce_payment_complete_order_status', 'change_status_to_quote_if_applicable', 10, 2);
  function change_status_to_quote_if_applicable($order_status, $order_id) { 
      $order = new WC_Order($order_id);
      $items = $order-&gt;get_items();
      foreach ($items as $item) {
          $product = get_product($item['product_id']);
          if(product_available_for_quote($product)){
              return 'quote';
          }
      }
      return $order_status;
  }
  </code></pre>
  
  <p>Now I want to recieve an email whenever an order is recieved that has been given the status quote. I've created a plugin based on this helpful article: <a href="http://www.skyverge.com/blog/how-to-add-a-custom-woocommerce-email/" rel="noreferrer">http://www.skyverge.com/blog/how-to-add-a-custom-woocommerce-email/</a></p>
  
  <p>My plugin is basically copied from the article, I've just changed the contents of the email. What I wanted to change is what triggers the email.</p>
  
  <p>The plugin in the article has this:</p>
  
  <pre><code>// Trigger on new paid orders
  add_action( 'woocommerce_order_status_pending_to_processing_notification', array( $this, 'trigger' ) );
  add_action( 'woocommerce_order_status_failed_to_processing_notification',  array( $this, 'trigger' ) );
  </code></pre>
  
  <p>And I want the email to be triggered when an order gets the status 'quote'. I did this:</p>
  
  <pre><code>// Trigger on new quote orders
  add_action( 'woocommerce_order_status_pending_to_quote', array( $this, 'trigger' ) );
  </code></pre>
  
  <p>Nothing happens when an order gets the 'quote' status. I've checked class-wc-order.php and specifically the function <code>update_status</code>, since that's where the <code>woocommerce_order_status_.$this-&gt;status._to_.$new_status-&gt;slug</code> is fired. I did an error_log to see that the <code>woocommerce_order_status_pending_to_quote</code> action exists, and it does. But my trigger function in my plugin is never run.</p>
  
  <p>Any ideas? I've tried loads of different hooks but I can't seem to get the trigger function to run.</p>
  
  <p>Thanks a lot!</p>