Only enable notification ack button if there are any unread ones

src/views/notifications.html

@@ -3,7 +3,7 @@
   <div class="text-left">
     <h1>{{ 'notifications.title' | tr }}
 
-      <button class="btn btn-primary btn-outline pull-right" ng-click="clearAll()" ng-disabled="clearAllBusy"><i class="fa fa-circle-notch fa-spin" ng-show="clearAllBusy"></i><i class="fa fa-check" ng-hide="clearAllBusy"></i> {{ 'notifications.markAllAsRead' | tr }}</button>
+      <button class="btn btn-primary btn-outline pull-right" ng-click="clearAll()" ng-disabled="!hasUnread || clearAllBusy"><i class="fa fa-circle-notch fa-spin" ng-show="clearAllBusy"></i><i class="fa fa-check" ng-hide="clearAllBusy"></i> {{ 'notifications.markAllAsRead' | tr }}</button>
       <button class="btn btn-default btn-outline pull-right" ng-click="showNextPage()" ng-disabled="busy || perPage > notifications.length">{{ 'main.pagination.next' | tr }} <i class="fa fa-angle-double-right"></i></button>
       <button class="btn btn-default btn-outline pull-right" ng-click="showPrevPage()" ng-disabled="busy || currentPage <= 1"><i class="fa fa-angle-double-left"></i> {{ 'main.pagination.prev' | tr }}</button>
     </h1>

src/views/notifications.js

@@ -9,6 +9,7 @@ angular.module('Application').controller('NotificationsController', ['$scope', '
     $scope.notifications = [];
     $scope.activeNotification = null;
     $scope.busy = true;
+    $scope.hasUnread = false;
     $scope.currentPage = 1;
     $scope.perPage = 20;
 
@@ -27,6 +28,7 @@ angular.module('Application').controller('NotificationsController', ['$scope', '
             });
 
             $scope.notifications = result;
+            $scope.hasUnread = !!result.find(function (n) { return !n.acknowledged; });
 
             $scope.busy = false;
         });
@@ -76,6 +78,7 @@ angular.module('Application').controller('NotificationsController', ['$scope', '
         }, function (error) {
             if (error) console.error(error);
 
+            $scope.hasUnread = false;
             $scope.clearAllBusy = false;
         });
     };