Write modern-style urls

- Proper use of include
- Defining namespaces (I do not use them for now because many urls are
  going to change)
- Do not try to reverse with old-style references: 'cof.views.XXX'

cof/templates/registration_form.html

@@ -7,7 +7,7 @@
     {% else %}
         <h3>Inscription d'un nouveau compte (extérieur ?)</h3>
     {% endif %}
-    <form role="form" id="profile" method="post" action="{% url 'cof.views.registration' %}">
+    <form role="form" id="profile" method="post" action="{% url 'registration' %}">
         {% csrf_token %}
         <table>
             {{ user_form | bootstrap }}