Tickets: support a single name field for organizations (instead of first name + last name)

The ticket order form currently requires separate **first name** and **last name** fields. This is problematic for tickets purchased on behalf of organizations or companies, which have a single name.

## Requested behaviour

Support a single **name** field (or an "organization name" field) as an alternative to the first/last name split. This may need to be configurable per event or per product type.

## Background

Requested in customer feedback.