Add a customer

Customers are created from a job or a quote, or from + Add. Only the display name is required. Add what you have:
- Billing name and contact name
- Email, billing email, mobile
- ABN (checked for a valid format, warned if odd, never blocked)
- Billing address
- Default payment terms in days
- Default deposit, percent or flat
- Preferred contact: email, SMS or phone
Recpt warns if a similar name or the same phone already exists, and lets you save anyway.