Enable adding voucher from the review screen

pinaxcon/templates/registrasion/review.html

@@ -9,7 +9,22 @@
   t-shirts and social event tickets.
 {% endblock %}
 
+{% block scripts_extra %}
+  {{ voucher_form.media.js }}
+
+  <script type="text/javascript">
+    function showVoucherForm() {
+      $("#voucher-form").show();
+      $("#voucher-form-button").hide();
+    }
+
+  </script>
+
+{% endblock %}
+
+
 {% block content %}
+  <button id="voucher-form-button" class="btn" onclick="showVoucherForm()">Enter voucher code</button>
 
   {% items_pending as pending %}
   {% if pending %}