kivy: InvoiceDialog: make LN invoice QR code scannable
kivy: InvoiceDialog: make LN invoice QR code scannable

Don't show the text and the QR code together, only the QR code:
the text takes up too much space, which make the QR hard to scan.

pooler/electrum-ltc,wakiyamap/electrum-mona,pooler/electrum-ltc,wakiyamap/electrum-mona,spesmilo/electrum,pooler/electrum-ltc,spesmilo/electrum,wakiyamap/electrum-mona,pooler/electrum-ltc,spesmilo/electrum,spesmilo/electrum,wakiyamap/electrum-mona