Update all references to "Bitcoin" and "Electrum" in the UI and codebase to "Palladium" and "Pallectrum" respectively. This includes network names, wallet types, error messages, and other user-facing text. Also updates the BIP21 URI scheme from 'bitcoin' to 'palladium'.
qml: add signals for QEQRScanner and fallbacks, add QEBytes container type
so we can pass along byte arrays between QML and python, port qr scan
occurrences to new signals.
