Populate "description" on line items

Problem/Motivation

our clients are having trouble with reconciliation because the Line Items in Authorize.net don't carry much information.

Steps to reproduce

There's a "Description" field on Line Items in Authorize. It never gets populated by transactions from this module.

Proposed resolution

Add a default description and invoke an alter hook.

Remaining tasks

Review patch.

User interface changes

None

API changes

Adds a new hook.

Data model changes

None