Fixed change payment method on cart.php with ajax

On cart.php you can now switch back and forth between credit card and
P.O. and it updates without a page refresh.

also included link to new checkout-cc.php page for credit card purchases
Pre-K Curriculum form

Added the correct product form for Pre-K (not connected to cart yet)
and moved the main curriculum form to Kindergarten (which is what it
was for in the first place).