Litle account updater support

 - Adds account updater XML to the commerce_litle_test module.
 - Some other improvements to the commerce_litle_test module.
 - Adds a hook to alter the end date when creating a sustainer series.
 - Adds a setting to Litle configuration to extend new sustainers by one month.
 - Adds functionality to the Litle module to update a sustainer series when Litle sends account updater information.
 - Refactored the billing update code so that Account Updater can use it.

Should the code here that checks for credit card or bank account numbers be removed? Then only the cardonfile data needs to be verified and shown; reasons:
* The 'accNum' value is only used in Litle, other bank account processors will use different field names.
* We could include a drupal_alter to allow non-cardonfile processers to still set a value.