Use historical price for older blocks and transactions

frontend/src/app/services/api.service.ts

@@ -6,6 +6,7 @@ import { Observable } from 'rxjs';
 import { StateService } from './state.service';
 import { WebsocketResponse } from '../interfaces/websocket.interface';
 import { Outspend, Transaction } from '../interfaces/electrs.interface';
+import { Conversion } from './price.service';
 
 @Injectable({
   providedIn: 'root'
@@ -303,4 +304,8 @@ export class ApiService {
         (style     !== undefined ? `?style=${style}` : '')
     );
   }
+
+  getHistoricalPrice$(): Observable<Conversion> {
+    return this.httpClient.get<Conversion>( this.apiBaseUrl + this.apiBasePath + '/api/v1/historical-price');
+  }
 }