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.
Optimal Payment: Make account mandatory field

The Optimal Payments gateway requires an accountNum field as part of the
credentials. This commit makes it a mandatory field while also deprecating
the existing login field which is called store_id in Optimal vernacular.

Closes #1307, closes #1309.
Worldpay: Improve address defaulting

We've seen that Worldpay can, without warning, turn on the requirement
for address1 and city.  Previously, we were defaulting things like
postal_code and state.  Now we default more of the address fields if
they're not specified.

In theory, this should help some customers, it shouldn't hurt any
existing customers, and it should help customers down the road if
Worldpay changes the address requirements on an account.

Closes #1310.