add a sorted_clins property for clin sorting logic

CLINS have a special ordering:
 - First, they are sorted by the last three digits
 - Then, they are sorted by the first digit

Trying to add CLIN sorting logic to the relationship field in the task
order proved to be more challenging than expected. So, a separate
property was defined in order to access the clins in sorted order.

templates/fragments/task_order_review.html

@@ -49,7 +49,7 @@
             </thead>
 
             <tbody>
-              {% for clin in task_order.clins %}
+              {% for clin in task_order.sorted_clins %}
               <tr>
                 <td>{{ clin.number }}</td>
                 <td>{{ clin.type }}</td>