Implement attachment migration for attachments
Add support for more information stored about the patches in the individual
patche files with a Javadoc style syntax

Add SQL patch file and update the main install SQL (MySQL) script to
transfer messages, responses, and notes into the new ticket_thread table.
For new installations, transfer is not necessary because there are no
messages

Replace the ticket_{message,response,note} tables with a single
ticket_thread table that will contain data for all three current message
types. This simplifies much of the ticket thread code and paves the way for
other types of messages in the future.

Track assigned department, team, staff, and help topic when the ticket event
occurs. This will greatly help in correlation of various reports and queries

Also start plowing the way toward incremental database updates using a
patching technique. The hash of the main install SQL script for a respective
database will be used to track the signature of the database currently. The
signature will be stored in %config::schema_signature, and the main.inc.php
script can simply check the value in the schema against the value known to
the source code to be the signature the code expects. Should the two
signatures differ, patches in the setup/inc/sql/patches folder should exist
and be executed to assist in incrementally upgrading the database to the
new-current schema version.

Assignees refactored.

Pull request #35-40. Co-reviewed by Jared & Peter on 04.01.12