Draw more attention to the need to select complimentary items

A big complaint from 2017 was that people overlooked things like
shirts and dinner tickets as those are complimentary, so they assumed
they didn't need to choose them.

This change adds some labels and some explanatory text to try to make
this more clear.

pinaxcon/templates/registrasion/discount_list.html

@@ -1,5 +1,6 @@
 {% if discounts %}
-<h3>Discounts and Complimentary Items</h3>
+<div class="alert-success">
+<h3 class="label-success">Discounts and Complimentary Items</h3>
 <div class="vertical-small"></div>
 
   {% regroup discounts by discount.description as discounts_grouped %}
@@ -11,9 +12,12 @@
     {% endfor %}
   </ul>
   {% endfor %}
-  <blockquote><small>Any applicable discounts will be applied automatically when you check out.</small></blockquote>
+  <blockquote>
+      <small>Note that you must choose your items below, even if they are complimentary.</small>
+      <small>Any applicable discounts will be applied automatically when you check out.</small>
+  </blockquote>
 
   <hr />
-
+</div>
 
 {% endif %}

pinaxcon/templates/registrasion/review.html

@@ -33,8 +33,8 @@
 
   {% missing_categories as missing %}
   {% if missing %}
-
+  <div class="alert-warning">
-    <p>
+    <p class="label-warning">
       <strong>You have <em>not</em> selected anything from the following
         categories. If your ticket includes any of these, you still need to
         make a selection:
@@ -42,7 +42,7 @@
     </p>
 
     {% include "registrasion/_category_list.html" with categories=missing %}
-
+  </div>
   {% endif %}
 
   <p>