Detect RBF-transactions and offer to track them.

fixes #78

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

@@ -1,6 +1,14 @@
 <div class="container-xl">
 
   <div class="title-block">
+    <div *ngIf="rbfTransaction" class="alert alert-mempool" role="alert">
+      This transaction has been replaced by:
+      <a class="alert-link" [routerLink]="['/tx/' | relativeUrl, rbfTransaction.txid]" [state]="{ data: rbfTransaction }">
+        <span class="d-inline d-lg-none">{{ rbfTransaction.txid | shortenString : 24 }}</span>
+        <span class="d-none d-lg-inline">{{ rbfTransaction.txid }}</span>
+      </a>
+    </div>
+  
     <h1 class="float-left mr-3 mb-md-3">Transaction</h1>
 
     <ng-template [ngIf]="tx?.status?.confirmed">