Merge pull request #355 from superrbstudio/1.2/develop

Fix for adding product variants to cart
Made address validation more obvious

When validating an address field any errors produced will be attributed
to either billing or shipping information. This is intended to cleanup
any confusion there may be for users thinking they have completed fields
they haven't.
Products & best sellers plugin update
Merge branch '1.2/develop' of https://github.com/firesale/firesale into 1.2/develop
Added a new method to retrieve cart contents as a json object