bugfix: qr-code: preserve state when switching between input modes

[nikochiko]

input modes: text/url, image, and (wip) vcard

Q/A checklist

• Do a code review of the changes
• Add any new dependencies to poetry & export to requirementst.txt (poetry export -o requirements.txt)
• Carefully think about the stuff that might break because of this change
• The relevant pages still run when you press submit
• If you added new settings / knobs, the values get saved if you save it on the UI
• The API for those pages still work (API tab)
• The public API interface doesn't change if you didn't want it to (check API tab > docs page)
• Do your UI changes (if applicable) look acceptable on mobile?

[devxpy]

This has been implemented in another commit to account for the new fields, thanks for the idea!

https://github.com/dara-network/gooey-server/blob/00dac8de55463500ba920bcc0c49258417de96e0/recipes/QRCodeGenerator.py#L526