Add option to remove events/regforms

[tomasr8]

• Adds an option to permanently delete events/regforms from the app
• Adds a confirm modal and optimizes the modal context to prevent unnecessary re-renders.
• Some internal improvements for useLiveQuery and checking whether it is still loading
• Relaxes validation for participant QR code data - for some reason eventId is sent as a string. I added a workaround in the app since changing this in Indico could break the old app.