Show QR code in fullscreen

[heinezen]

Feature description

Add an option to show a generated QR code in fullscreen view.

Problem and motivation

Might be interesting for shops using a tablet or another digital screen.

[fynngodau]

There is a similar wishlist item for a similar request for the mobile apps: https://github.com/corona-warn-app/cwa-wishlist/issues/458

[przybciu]

Can I work on this? I already have an idea