feat(purchase.html): FoxyCart taxable downloads.

FoxyCart is now used to process payments and apply sales tax in
applicable states.

Don't change the HMACS, or generate them on your own.
chore(purchase.html): Readd former purchase page

Apparently we need the link to Wufoo to stay for a while longer
until the move over to FoxyCart is completed.
chore(foxy_purchase.html): Rewording, add license agreement.
chore(foxy_purchase_discount.html): Add page for discount purchases

This page will allow purchasing for those who have the 30% discount
enabled.
fix(foxy_purchase*.html): Add quantity field to purchase form.

Although the quantity is now sent, whenever the user presses
the "Agree & Purchase" button, the current quantity in the car will be incremented.
fix(foxy_purchase_discount.html): Forgot the hidden "quantity" field
Purchase link now redirects to FoxyCart page. Ready for liftoff...
Merge branch 'feature/foxy-cart' into gh-pages