ability to specify sold to contact at rate plan level

[Renaldo]

We require the ability to define a sold to contact at rate plan level.

A suscription is created for several product rate plans, each with differing sold-to locations, i.e. the servce is consumed by consumers in different locations.

This means that vat / tax is calculated based on the sold-to contact at the rate plan level (if specified), otherwise, the subscription sold-to is used to determine the vat / tax obligation.

It should also be possible to display this subscription rate plan contact (sold-to) on the invoice.

[nharlow]

This is an interesting idea. It would require a number of changes as to how tax is currently calculated. However, charge-level taxation is an increasingly common request, especially with larger, more sophisticated customers. I'll investigate this.