add be2bill (www.be2bill.com) payment gateway

Hi,

I created a new adapter for the be2bill payment gateway (www.be2bill.com). This is a french payment gateway.
The unit and remote tests are functional.

All the possibilities of the be2bill payment gateway are not working yet but I was able to use it for some payments (and recurring payments) in my project.

Thank you for your hard work on this great project ! I'm happy to make a small contribution on it.