Add a QR Code in the vote page

[renaudjenny]

It could be nice to add a QR Code in the top right of the page as it's useful for mobile device to scan the code and be redirected directly to the vote page instead of navigating through Grooming Session ➡️ User Story ➡️ Vote.
An interesting library to get the code from is this one: https://github.com/nayuki/QR-Code-generator
There is a Rust version 😏...