Add user signup form and implement signup view; enhance message display in templates

base/templates/registration/login.html

@@ -2,5 +2,8 @@
 {% load form %}
 {% block content %}
     <h1>Connexion</h1>
+    <p>
+        <a href="{% url "signup" %}">Créer un compte</a>
+    </p>
     {% form form submit="Se connecter" %}
     {% endblock content %}