Added the ability to export and import Stock By Attributes data for item...

...s

that already are being tracked by SBA.  Also incorporated the correction
for Basic Attribute export so that the products option types would be
correct.  Shows user readable information for items that have only one option type. (I.e., color); however, if there is more than one option type, then verbiage will not yet download properly, but quantities will be correctly updated on import.
Option to use SBA is dependent on the existence of the PRODUCTS WITH ATTRIBUTES STOCK  table, that the table has only 5 columns, and that the columns are titled: stock_id, product_id, stock_attributes, quantity, and sort.  If this is not the case, then can not export nor import on this option.  If you have the ability to stock by attributes, but do not have this option, then may need more information made available to incorporate the functionality.  (I.e., the table(s) associated, the field names, a download location for the plugin that provided this functionality for your Zen-Cart, etc.)