Adding X-button to close mempool blocks.

frontend/src/app/components/mempool-block/mempool-block.component.html

@@ -1,9 +1,12 @@
 <div class="container-xl" *ngIf="mempoolBlock$ | async as mempoolBlock">
 
   <div class="title-block">
-    <h1>{{ getGetOrdinal() }}</h1>
+    <h1 class="float-left">{{ getGetOrdinal() }}</h1>
+    <button [routerLink]="['/' | relativeUrl]" class="btn btn-sm float-right mr-2">&#10005;</button>
   </div>
 
+  <div class="clearfix"></div>
+
   <div class="box">
     <div class="row">
       <div class="col-sm">