Litle: Support passing optional fields in token based transactions

  * Added a LitleCardToken class to make working with tokens similar to credit cards.
  * Updated existing tests to use the new LitleCardToken class in calls to authorize and purchase.
  * Added missing certification tests for explicit token registration.
  * Updated existing certification tests to use the latest documented data.
  * Added support for processing a credit transaction with a token as well as a previous transaction id (identification).
  * Updated certification specs based on direct feedback from Litle. (some required data was missing).
  * Removed ability to pass just a string for a token. Must use the LitleCardToken class.
Merge pull request #3 from LessonPlanet/litle/allow-card-token-fields-to-be-set-for-token-based-transactions

[#43956839] Added support for passing optional fields in Litle token based transactions