Add "extra panels" customization hook to product details template.

tailbone/templates/products/read.mako

@@ -90,6 +90,8 @@
       </div>
     </div>
 
+    ${self.extra_left_panels()}
+
   </div> <!-- left column -->
 
   <div class="panel-wrapper"> <!-- right column -->
@@ -154,9 +156,15 @@
       </div>
     </div>
 
+    ${self.extra_right_panels()}
+
   </div> <!-- right column -->
 
   % if buttons:
       ${buttons|n}
   % endif
 </div>
+
+<%def name="extra_left_panels()"></%def>
+
+<%def name="extra_right_panels()"></%def>