Adding ship_address_country and bill_address_country promo rule

Added two new promotion rules:
1) Ship Address Country 
    Description: Only valid for this country's shipping address
2) Bill Address Country
    Description: Only valid for this country's billing address
3) Added country drop down in the rule defaulted to United States.
4) The coupon would be applied only if the billing/shipping address of the order matches the selected country in its corresponding rule.