Prometheus - Donation and payment store

As per usual, there's never an update without several patches following shortly after:

1. Fixed part two of the previous issue: A credits price had to be set, or the package would be considered free instead of custom price if "only credits" is enabled.

Modified files

Web

1. inc/functions.php
2. inc/classes/gateways.class.php
3. inc/classes/store.class.php