Customize the field name, firstname and email

**Is your feature request related to a problem? Please describe.**
For Devoxx4kids, we organize events for children, so the ticket are bought by the parents and the children don't have mail address.
So I would like to customize the labels to rename "first name" as "child first name" and remove or hide the mail address.

**Describe the solution you'd like**
Is could be separate label for i18n to configure them or just display the first 3 fields as the next ones.