backups: add ui for filename encryption

src/views/app.html

@@ -400,6 +400,12 @@
             <input type="text" class="form-control" ng-model="importBackup.password" id="inputImportBackupPassword" ng-disabled="importBackup.busy" ng-required="importBackup.encrypted" placeholder="Passphrase used to encrypt the backups">
           </div>
 
+          <div class="checkbox" ng-show="importBackup.format === 'rsync' && importBackup.password !== ''">
+            <label>
+              <input type="checkbox" ng-model="importBackup.encryptedFilenames">{{ 'backups.configureBackupStorage.encryptedFilenames' | tr }}</input>
+            </label>
+          </div>
+
           <input class="ng-hide" type="submit" ng-disabled="importBackupForm.$invalid"/>
         </form>
       </div>