Add L-BTC sponsor support.

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

@@ -1 +1,4 @@
-<canvas #canvas></canvas>
+<div class="holder" [ngStyle]="{'width': size, 'height': size}">
+  <img *ngIf="imageUrl" [src]="imageUrl">
+  <canvas #canvas></canvas>
+</div>

frontend/src/app/components/qrcode/qrcode.component.scss

@@ -0,0 +1,11 @@
+img {
+  position: absolute;
+  top: 67px;
+  left: 67px;
+  width: 65px;
+  height: 65px;
+}
+
+.holder {
+  position: relative;
+}

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

@@ -9,6 +9,7 @@ import * as QRCode from 'qrcode/build/qrcode.js';
 export class QrcodeComponent implements AfterViewInit {
   @Input() data: string;
   @Input() size = 125;
+  @Input() imageUrl: string;
   @ViewChild('canvas') canvas: ElementRef;
 
   qrcodeObject: any;