use Chosen for country select on credit card form

this is a follow-up to #1802

Chosen allows you to easily search for the option you want without having to manually search through the entire list:

![screen shot 2013-12-27 at 11 49 03 am](https://f.cloud.github.com/assets/688886/1815635/4d5eae3c-6f1f-11e3-9bb4-ae970d2c2d78.png)