participants: added support for year of birth

dav_events/templates/dav_events/includes/participant_form.html

@@ -21,12 +21,15 @@
     </div>
 </div>
 <div class="row">
-    <div class="col-sm-6">
+    <div class="col-sm-4">
         {% bootstrap_field form.email_address %}
     </div>
-    <div class="col-sm-6">
+    <div class="col-sm-4">
         {% bootstrap_field form.phone_number %}
     </div>
+    <div class="col-sm-4">
+        {% bootstrap_field form.year_of_birth %}
+    </div>
 </div>
 <div class="row">
     <div class="col-sm-3">