Drops deleted workspace roles from /admin/users/ (#407)

tracim/tracim/model/serializers.py

         id = workspace.workspace_id,
         label = workspace.label,  # FIXME - 2015-08-20 - remove this property
         name = workspace.label,  # use name instead of label
+        is_deleted=workspace.is_deleted,
         url = context.url('/workspaces/{}'.format(workspace.workspace_id))
     )
     return result

tracim/tracim/templates/admin/user_getone.mak

                         </tr>
                     </thead>
                     % for role in result.user.roles:
+                        % if not role.workspace.is_deleted:
                         <%
                             enable_link = '/admin/users/{user}/workspaces/{workspace}/enable_notifications?next_url=/admin/users/{user}'
                             disable_link = '/admin/users/{user}/workspaces/{workspace}/disable_notifications?next_url=/admin/users/{user}'
                         %>
                         ${TABLE_ROW.USER_ROLE_IN_WORKSPACE(fake_api.current_user, role, show_id=True, enable_link=enable_link, disable_link=disable_link)}
+                        % endif
                     % endfor
                 </table>
             % endif