Switched from error_code to status_code for result check

Payment module now checks against status_code instead of error_code to
determine whether the payment has been successful
Fixed PaychoiceHttpClient non 200 HTTP response

PaychoiceHttpClient was only checking for a non 200 response when it
should have been checking for 500.

These changes were initally made in
https://github.com/paychoice/paychoice-php/blame/015681ddd391999d2d91c4a157ba851e92dbff60/lib/PaychoiceHttpClient.php