Authorize.net Card Present Gateway

Support for the Authorize.net Card Present interface.  The core work was done by the folks over at Square (https://github.com/square).  It appears they are no longer using their branch, so I merged in the shopify/active_merchant master branch and also updated the interface to include a few more features.  

New features include:

* Returning the card_type from the Authorize.net response
* Returning the card_number from the Authorize.net response
* Added support for track1 data
* Fixed bug in the expdate method
* Remote testing now uses a testing endpoint instead of the "live" endpoint