Add GST option when creating invoices where it currently says VAT

[zach-sb]

In Australia we have GST (Goods and Services Tax). From a very light look into it it seems more or less equivalent to VAT. When creating an invoice could we have it so that if we are using AUD, it says GST instead of VAT? Or at least give us that option as a drop down?

(Ideally, same deal where it says VATIN, in Australia we have our Australian business number (ABN), but this is less of an issue as I don't think it shows on the invoice itself)