Add loading spinner in /blocks page

frontend/src/app/components/blocks-list/blocks-list.component.html

@@ -2,6 +2,7 @@
 
 <div class="container-xl" [class]="widget ? 'widget' : 'full-height'">
   <h1 *ngIf="!widget" class="float-left" i18n="master-page.blocks">Blocks</h1>
+  <div *ngIf="!widget && isLoading" class="spinner-border ml-3" role="status"></div>
 
   <div class="clearfix"></div>