Add wiredump_device and PayPage registration support for litle

This patch adds support for `wiredump_device` and PayPage to the Litle gateway:

1. Allow to pass a `paypageRegistrationId` in the `store` call, instead of a credit card.

2. By specifying a wiredump device, such as:

```
ActiveMerchant::Billing::LitleGateway.wiredump_device = File.open('/var/tmp/litle.log', 'w')
```
    
the device will now be properly passed to the LitleOnline gem for logging.
    
The LitleOnline gem uses its own connection mechanism and the logging hook will be available only in versions more recent than 8.15.


Testing Done: tested the integration with the Kill Bill Litle plugin (see https://github.com/killbill/killbill-litle-plugin and http://kill-bill.org).