feat: QR scanning audible feedback

[grablair]

To continue to improve the QR scanning, this change introduces audible feedback sounds to the QR scanning process. The notification sounds are small .wav files, and are royalty-free.

The sounds are:

1. A beep when an attendee ID is read successfully (sounds like a store scanner "beep")
2. A quick chime when the attendee is successfully checked in
3. A quick error double-tone if the check-in fails or the attendee is already checked in

Since not everyone will prefer to have sounds on, this also adds a sound-toggling button to the QR scanning screen. This setting is saved to local storage to the user doesn't need to change the setting between browser sessions.

Checklist

• I have read the contributing guidelines.
• My code is of good quality and follows the coding standards of the project.
• I have tested my changes, and they work as expected.

Thank you for your contribution! 🎉

[daveearley]

Awesome, thank you! Nice feature.