allow us to require an email for each guest in a reservation

Our members love to bring guests (at our club they do not have any membership), and we ask guests to sign waivers. But we have no way to cross-check between the guest report and the guest waiver report to ensure all guests have signed waivers. 

Also, there are times when we need to contact a guest, for instance when they've played more times per month than our policy allows - we'd like to convert them to a member in some cases. But we need an email to do that.