Add card types to schema

Add payment/card/type endpoint to the schema, as per the c# wrapper (public in that project although undocumented on api.7digital.com).

Only slightly strange thing is the response has e.g.:

    <cardTypes>
        <cardType id="MASTERCARD">Mastercard</cardType>
        <cardType id="MAESTRO">Maestro</cardType>
        ....
    </cardTypes>

which means the JSON comes out like this - the underscore is a bit unclear maybe?

    { cardType: [
        { _: 'Maestro', id: 'MAESTRO' },
        { _: 'Mastercard', id: 'MASTERCARD' },
        .... 
    ]}