Define the SnapPay HPP settings form

We already have environment selection and need to add at least:

• Account ID
• Merchant ID
• Email receipt

It's unclear of the Customer ID is something related to the SnapPay account or the ID of the customer (i.e. uid) in Drupal itself.

Committed with an additional boolean for enabling / disabling the CVV field.

Automatically closed - issue fixed for 2 weeks with no activity.