style(volumes): replace label 'Dangling' with 'Unused' (#1052)

app/components/volumes/volumes.html

@@ -38,7 +38,7 @@
           Attached
         </label>
         <label class="btn btn-primary" ng-model="state.danglingVolumesOnly" uib-btn-radio="true">
-          Dangling
+          Unused
         </label>
       </span>
     </rd-widget-taskbar>
@@ -85,7 +85,7 @@
               <td><input type="checkbox" ng-model="volume.Checked" ng-change="selectItem(volume)"/></td>
               <td>
                 <a ui-sref="volume({id: volume.Id})" class="monospaced">{{ volume.Id|truncate:25 }}</a>
-                <span style="margin-left: 10px;" class="label label-warning image-tag" ng-if="volume.dangling">Dangling</span></td>
+                <span style="margin-left: 10px;" class="label label-warning image-tag" ng-if="volume.dangling">Unused</span></td>
               </td>
               <td>{{ volume.Driver }}</td>
               <td>{{ volume.Mountpoint | truncatelr }}</td>