Adding a global websocket loader observable.

fixes #95

frontend/src/app/components/blockchain/blockchain.component.html

@@ -10,8 +10,7 @@
     <ng-template [ngIf]="isLoading">
       <div class="loading-block">
         <h3>Waiting for blocks...</h3>
-        <br>
-        <div class="spinner-border text-light"></div>
+        <div class="spinner-border text-light mt-2"></div>
       </div>
     </ng-template>