Microdata JSON LD : add combinations / category page support in .tpl

[fdonnet]

Schema access (https version)

Product description Regex to remove carriage returns (not allowed by Facebook or the schema.org def => JSON validity)

Product combinations support to create corresponding offers

• Not a perfect solution, but it will do the minimal job for Google
• Remove ean13 part because we cannot access this information in the smarty $combinations var. Only in another one (complexity). Keep mpn and sku for Google (reference or id).
• "condition" tag excluded for combination products but will work if you don't sell old or refurbished products.
• Rating (excluded for combinations) => see if we can take the info from the base product
• Stock quantity and price => OK
• Name (concat attribute) => OK
• Images = OK

Add support for category pages ItemList implementation that makes the link to product page. (better implementation than the normal proposition in the official classic theme, I think)

This PR is only to propose a not perfect solution for the product combinations (JSON -LD).