QR code - improve readability

[Talbatz]

qr code presented on "recive" scrren can be improved so that it would be picked up faster when being sanned.

current QR code is only 128x128 px - we can make it bigger.

When downloading the qr code and / or sharing it, it becomes unscannable when being displayed on a dark background (like slack darkmode, for example) a solution for that can be adding a small white background, in the image file of the qr.