updated the code to be compatible with 1-3-stable

This PR includes fixes for:
1 Required javascripts, id conflicts from address to payment for one page checkout form as it was not loading any of the payment methods properly on the page. 
2 Added a partial which overrides spree's partial to be sure that user does not see/ reach the old checkout flow intentionally. 
3 Updated gemspec to updated dependencies.
4 Includes factories for specs.

I didn't see 1-3-stable branch so had to send pull request(PR) on master. So, far so good. I can ensure that everything is working smoothly in production.