add sound item in diffusions; move programs.Sound's attribute 'remove' into the type + update its public attribute based on diffusion publication

cms/templates/cms/snippets/sound_list_item.html

@@ -0,0 +1,13 @@
+{% load static %}
+
+{# TODO: complete archive podcast -> info #}
+<a class="list_item sound" onclick="player.playlist.add(new Sound(
+        title='{{ item.name|escape }}',
+        detail='{{ item.detail_url }}',
+        stream='{% static item.path %}'));">
+    <h3>{{ item.name }}</h3>
+    <span class="info">
+        {{ duration.date|date:'H:i:s' }}
+    </span>
+</a>
+