Reorganize  code that interfaces to updated wp-e-commerce.js

Before this code gets into the wild it deserves some clean-up.  

* cleaned the special purpose code out of the service function wpsc_update_customer_meta_ajax, removed checkout specific logic from meta update routine wpsc_update_customer_meta_ajax
* new file to hold localization and AJAX processing routines that support wp-e-commerce.js
* moved hook that processes meta on change on shipping same as billing into meta utility file,  it is now with other hooks that do similar meta processing
* use ajax action specifically for updating information supplied by customer on checkout or user log form
* removed checkout specific logic from general purpose customer meta update function
*removed JavaScript localizations from country class and moved them the the file that handles all the interfaces to the wp-e-commerce.js
* moved checkout localizations required by the wp-e-commerce.js into the module that handles the interface to the wp-e-commerce.js
* moved functions that provide information about checkout form element status to the js routine in the wp-e-commerce.js interface module
* include file that handles the localization and ajax interface to wp-e-commerce.js

*addresses issue #1138*