Wording on discounts on the form pages shows the reason for the discount.

Fixes #6.

pinaxcon/templates/registrasion/discount_list.html

@@ -1,7 +1,7 @@
 {% if discounts %}
   <ul>
     {% for discount in discounts %}
-      <li>{{ discount.quantity }} &times; {{ discount.clause }}</li>
+      <li>{{ discount.discount.description }}: {{ discount.quantity }} &times; {{ discount.clause }}</li>
     {% endfor %}
   </ul>
 {% endif %}