Shopping cart module

[einkoro]

I already have a cart module that I use at work but its very specific to: 1) PayFlow Pro 2) Our licensing system. We should make a more general purpose cart at some point as I'm sure it will come up in client work.

[einkoro]

It has been somewhat generalized to support FAC and PPPFP but could still be improved. The licensing system has to be abstracted to be much more general.