[Intervention] Revocations files optional #4

* makes revocation file upload optional
 * adds overview about revocations to intervention index
 * adds/updates translations

intervention/templates/intervention/detail/includes/revocation.html

@@ -50,9 +50,11 @@
                 </td>
                 <td class="align-middle">{{ rev.comment }}</td>
                 <td class="align-middle">
-                    <a href="{% url 'doc-open' rev.document.id %}">
-                        {{ rev.document.file }}
-                    </a>
+                    {% if rev.document %}
+                        <a href="{% url 'doc-open' rev.document.id %}">
+                            {{ rev.document.file }}
+                        </a>
+                    {% endif %}
                 </td>
                 <td>
                     {% if is_default_member and has_access  %}