provide key on blockModel for angularJS performance optimization

src/Umbraco.Web.UI.Client/src/common/services/blockeditor.service.js

@@ -152,6 +152,7 @@
                 }
 
                 var blockModel = {};
+                blockModel.key = String.CreateGuid();
                 blockModel.config = angular.copy(blockConfiguration);
                 blockModel.labelInterpolator = $interpolate(blockModel.config.label);
 

src/Umbraco.Web.UI.Client/src/views/propertyeditors/blocklist/blocklist.component.html

@@ -5,7 +5,7 @@
 
         <div ui-sortable="vm.sortableOptions" ng-model="vm.blocks">
 
-            <div ng-repeat="blockItem in vm.blocks">
+            <div ng-repeat="blockItem in vm.blocks track by blockItem.key">
 
                 <button
                     type="button"