QR text editor: Allow scanning image files using the QR reader
QR text editor: Allow scanning image files using the QR reader

Uses the existing button for reading text files and adds the
ability to load an image file which will be scanned by the QR
scanner. It rejects multiple QR codes at the moment.

This also changes the show_critical used in the function to
show_error instead.

fyookball/electrum,fyookball/electrum,fyookball/electrum