Subscription refactoring to increase performance.

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

@@ -1,6 +1,6 @@
 <div class="mempool-blocks-container">
   <div class="flashing">
-    <ng-template ngFor let-projectedBlock [ngForOf]="mempoolBlocks" let-i="index" [ngForTrackBy]="trackByFn">
+    <ng-template ngFor let-projectedBlock [ngForOf]="mempoolBlocks$ | async" let-i="index" [ngForTrackBy]="trackByFn">
       <div class="bitcoin-block text-center mempool-block" id="mempool-block-{{ i }}" [ngStyle]="mempoolBlockStyles[i]">
         <a [routerLink]="['/mempool-block/' | relativeUrl, i]" class="blockLink">&nbsp;</a>
         <div class="block-body">