Transaction tracking revamped.

Blockchain block arrow.

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

@@ -10,6 +10,7 @@ import { StateService } from 'src/app/services/state.service';
 })
 export class BlockchainComponent implements OnInit, OnDestroy {
   @Input() position: 'middle' | 'top' = 'middle';
+  @Input() markHeight: number;
 
   txTrackingSubscription: Subscription;
   blocksSubscription: Subscription;