Currency can be pulled from shop.currency

Added currency (from shop.currency) to Product and Basket objects.

A few additional comments:
1. IMO OpenTag should NOT be included as part of the script, since UV can be used independently of OpenTag. Plus, some "customers" may already have OpenTag installed on their sites which may lead to duplicate tags if not careful.
2. The "Docs" say to use {% include 'universal-variable' %} but I believe this should be {% include 'uv' %} because the file is named "uv.liquid"
3. The TODO to "Loop through product tags" to create sub-sub-categories is a bad idea because of the various ways that tags are used in Shopify to control logic.