flows: FlowStageBinding: rename .flow to .target to fix select_subclasses()

passbook/admin/templates/administration/stage_binding/list.html

@@ -35,7 +35,7 @@
                 </tr>
             </thead>
             <tbody role="rowgroup">
-                {% regroup object_list by flow as grouped_bindings %}
+                {% regroup object_list by target as grouped_bindings %}
                 {% for flow in grouped_bindings %}
                     <tr role="role">
                         <td>
@@ -56,9 +56,9 @@
                         </td>
                         <th role="columnheader">
                             <div>
-                                <div>{{ binding.flow.slug }}</div>
+                                <div>{{ binding.target.slug }}</div>
                                 <small>
-                                    {{ binding.flow.name }}
+                                    {{ binding.target.name }}
                                 </small>
                             </div>
                         </th>