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.

electrum/gui/kivy/uix/dialogs/invoice_dialog.py

@@ -40,7 +40,9 @@ Builder.load_string('''
                 text: _('Invoice data')+ ':'
             RefLabel:
                 data: root.data
+                text: root.data[:40] + "..."
                 name: _('Data')
+                show_text_with_qr: False
             TopLabel:
                 text: _('Description') + ':'
             RefLabel: