Make the payment widget more compact

[dimarconicola]

• [x] reduce line height on the amount element
• [x] reduce letter spacing on the amount element
• [x] reduce margin on the currency select
• [x] reduce size of the qr code

BEFORE

AFTER

<div class="sc-dNLxif kNEaen" style="
    line-height: 1;">

letter-spacing: -0.2rem;

<div class="sc-frDJqD gKCCHP" style="
    margin: 0px; ">

<canvas id="react-qrcode-logo" height="460" width="460" style="height: 200px;width: 200px;padding: 2.17391%;background: rgb(255, 255, 255);"></canvas>