Authorize.Net: Fix amount formatting

Truncate refId (order_id) to 20 characters to pass schema validation.

Closes #1393.
Authorize.net: Truncate more fields

Now we truncate more fields to fit within Authorize.net's requirements
and pass schema validation.

Closes #1394.
Authorize.Net: Truncate invoiceNumber
Adyen: Add support for verify operation

Adyen supports a $0 authorization so we use that.  Relevant docs from
their PDF:

http://cl.ly/image/193d1U371T2X/content.png

Closes #1395.
DIBS Payment Services

This commit is maintained separate until DIBS setup a sandbox.
Code by @maxwhite