Add a customizable logo to QR (#1955)

* add QR_LOGO variable
* add logo to images folder
* css for overlaying logo on qr
* qr url on settings
* add qr url to global env
* add QR url input on theme tab in adminUI
* new component added
* use svg
* remove white border around logo in the QR

---------

Co-authored-by: Pavol Rusnak <pavol@rusnak.io>
Co-authored-by: dni ⚡ <office@dnilabs.com>

lnbits/static/css/base.css

@@ -535,3 +535,21 @@ video {
 .q-card code {
   overflow-wrap: break-word;
 }
+
+.qrcode__wrapper > canvas {
+  position: relative;
+  min-width: 100%;
+  min-height: 100%;
+}
+
+.qrcode__image {
+  width: 15%;
+  height: 15%;
+  overflow: hidden;
+  left: 50%;
+  overflow: hidden;
+  position: absolute;
+  top: 50%;
+  transform: translate(-50%, -50%);
+  padding: 0.3rem;
+}