Block changing data of the attendees

**Is your feature request related to a problem? Please describe.**
What happen if at the very last moment an attendee/responsible decides to change the name an email of an attendee? A nightmare to look where this ticket belongs to... and a problem in the registration :-/

**Describe the solution you'd like**
Probably one of the best solutions could be to "block" any change of any ticket before the conference starts. Like 3 days or 5 before (or even more)

**Describe alternatives you've considered**
I can't see any other alternative because basically the idea is to not accept any change after an specific date/time.

**Additional context**
N/A