Adding a favicon

I created a favicon and added it to the base template.

Resolves: #284

Signed-off-by: Matthieu Berjon <matthieu.berjon@inria.fr>

django/allgo/templates/base.html

@@ -15,6 +15,8 @@
     <link rel="stylesheet" type="text/css" href="{% static 'css/fontawesome-all.min.css' %}" media="all" charset="utf-8">
     <link rel="stylesheet" type="text/css" href="{% static 'css/allgo.css' %}" media="all" charset="utf-8">
     <link rel="stylesheet" type="text/css" href="{% static 'css/prism.css' %}" media="all" charset="utf-8">
+
+    <link rel="icon" type="image/png" href="{% static 'images/favicon.ico' %}" sizes="16x16">
     {% endblock %}
   </head>