shopping cart coupon checkout changes as suggested by Jason Bau
Merge pull request #4260 from edx/asadiqbal08/shoppingcart_coupon_checkout_changes_as_suggestedBy_JasonBau

shopping cart coupon checkout changes as suggested by Jason Bau
changes are made according to the suggesstions on PR#4172

changes made in the coupons file

changes in the coupons get_coupon_info view
fix merge conflict resolution error