feat: Option to show QR code for entries

[bhall7]

Feature description

I’d love the ability to show a QR code for each entry in 2FAS (maybe add “Show QR Code” as an additional long press menu item).

Motivation

This would be for instances where you’d like to add just one entry to another device without having to type in the whole secret key.

Acknowledgements

• [X] This issue is not a duplicate of an existing feature request.
• [X] I have chosen an appropriate title.
• [X] All requested information has been provided properly.