Validate form fields using element ID

... instead of form.<name> because the worldpay form doesn't
use the names.

As an aside; TODO: cleanup in this file is heavily needed.

Change-Id: If70f5669890dbcf0a0d9c81af6b8d3ed27aaa4a7
WorldPay Multiple Accounts

Yay; it works!

Lots of changed needed to local settings to get this
to work in production through... :p

Conflicts:
	tests/TestConfiguration.php

Change-Id: I20d614164bbf234886abdc926c5111614e4a6d3a