Add in stock notification. [Fixes #3200]

This will mark the structured data schema with "In Stock" if the item
is in stock.
Add currency to itemprop.

This will provide a more detailed price to users in search engine
results.

As an example.  In Canadian Dollars, it will display: CA$22.50 in the
Google search rankings instead of simply $22.50.
search -> ransack. Compat with TS [Fixes #3201]
Call ShippingMethod.available? with package as parameter, like the
method expects. [Fixes #3213] [Fixes #3215]