Add PK to %ticket_email_info.`id`

This patch partially reverts the previous database migration patch which
added a primary key to the table on the `thread_id` column. This column
cannot be used, because there may be multiple entries for thread_id = 0.

This also allows ticket_collaborator.isactive to be negative, as well as
adds the database portion of regex support for ticket filters.
filters: Implement regular expression matching
Drop `subject` and `body` from filters

They are only available for tickets arriving via the email channel. All
other channel (including email) use the new ticket form to record the
subject and body, which are mapped to the 'Issue Summary' and 'Issue
Details' fields respectively

Structure the drop-down list for the `what` column to be future-minded
concerning custom user data matching.
Merge pull request #481 from greezybacon/issue/email-thread-pk

Correct the PK on %ticket_email_info

Reviewed-By: Peter Rotich <peter@osticket.com>