Ensure contactID is in the parameters passed to the payment processor

There is some inconsistency in whether the payment processor receives the contact_id from the calling function. This is later passed to the alterProcessor hook.

In this case I am just standardising the behaviour from the participant form - I note that some payment processors seem to use $params['contactID'] so I am selecting this format (over $params['contact_id'] or the one I personally don't like $params['contactId'])