Addition: Paypal Express Sandbox Setup

[torvista]

I've made a start:
https://github.com/torvista/Zen_Cart-PayPal_Sandbox_setup

Please flesh it out. I'm pretty green on PayPal.

[scottcwilson]

This will deprecated by the PayPal REST update.

[drbyte]

Re-opening to keep it on radar because the REST module will need some sandbox documenting, and since the REST module doesn't incorporate Express, the Express sandbox still has relevance.

Finding the intersection of the two will be interesting...