IPv6 Client IP Addresses Fail Some Gateways

[judgej]

First raised on PR #10

If run with an IPv6 network, the example application will send the IPv6 address to the gateway. Some gateways only support IPv4, so some method of controlling this is needed.

[judgej]

Created a branch to expose the clientIp to the parameters form. Feel free to have a play. Some improvements would be:

• Retrieve the clientIp from the session if it is set, so it does not need to be changed every time a request is submitted.
• Do the same for the returnUrl, cancelUrl and notifyUrl - those are all reset every time you want to submit a request, even though the last submission of those fields are stored in the session.
• Move the setting of the clientIp param (including checking the session) into one place to avoid so much duplication. Effectively the detected client IP needs to be used as a default only, which is going to need a little more refactoring.

Have a play and see what you think.