Allow for VAT to be displayed on invoice version

WE need for invoices to corporate customers to show VAT, so need to allow vat to be shown on invoice versions, and also for the VAT level to be configured per line item.

Also, it would be handy for league fees to consist of multiple line items, as each line item may or may not have vat applicable (ie, a booking portion, which is vat exempt, plus a mangement portion which has vat on it).