Tax Invoice - AU

[Liz]

It has been requested before on this list, but I had an email exchange
with an over-zealous accounts clerk and decided to formalise a new AU
Tax Invoice.

I can't present a fully formed patch because I haven't solved the
duplicate GUID problem if I have the report from which I made this one
in business-reports.scm as well as the new one.

I'd like this to be able to have the Footer stylesheet applied
optionally but this seems to be greyed out in my menu when I test

It's attached to Bug 585101