Function to tell apart debit and credit card types

I've added the `kind` attribute to each card type and a public function to check whether a given type is a debit or a credit card. This is useful for cases such as to display or require additional information in payments with debit cards.

```javascript
$.payment.kind('visa'); //=> 'credit'
$.payment.kind('maestro'); //=> 'debit'
```

cc @cjoudrey @christianblais @jamesreggio 
Since I'm here, why not? :smile: