Payment Gateway Setup (PayTrail)

Overview
Please follow the instructions below to activate this gateway. If the payment gateway's interface has changed or if the screenshots (where applicable) look different, please let me know.
PayTrail - Setup
1: Sign up for a PayTrail account to receive your merchant id and password.
2: Log into your PayTrail account to create your authentication hash.
3: Enter applicable details in your Maian Cart admin area:

Sales > Payment Methods > PayTrail
PayTrail - Callback Url
The callback url for all operations is:

http://www.example.com/checkout/paytrail.php
https://www.example.com/checkout/paytrail.php (SSL)

Where 'example.com' is your own domain.
PayTrail - Sandbox
For testing, use the following test merchant ID and secret key:

Merchant ID: 13466
Merchant Secret: 6pKF4jkv97zmqBJ3ZL8gUw5DfT2NMQ

Test Bank Accounts:

Nordea
ID: 123456
Password: 1234

Osuuspankki
User ID: 123456
Password: 7890
Keynumber: Any number

Refer to the API docs for other test bank usernames and passwords.