Eway Rapid: Truncate some fields

Eway Rapid transactions fail if the parameters don't fit within the
required boundaries.  Therefore, we now truncate fields to their maximum
length.

In particular, we're now truncating order_id, description, billing_address1,
billing_address2, billing_city, shipping_address1, shipping_address_2,
shipping_city, and card_name.

Relevant docs:
http://api-portal.anypoint.mulesoft.com/eway/api/eway-rapid-31-api/docs/reference/transparent-redirect

Closes #1308.