Auth.Net CIM: Add extraOptions support

Adds 'extra options' (as defined by the Authorize.net CIM API) to the
gateway implementation for creating customer profile transactions.

Their API documentation describes extra options as follows:

> Information in name/value pair format that does
> not exist within CIM, such as customer IP address, etc.

The test demonstrates the effects of setting one of these extra options.

Closes #546.