Assignees refactored.

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

Feature/ticket open typeahead

Track history of tickets over time for snazzy dashboard reports

Feature/discard warning + ticket preview enhancements

Add CSV (Excel) export option to ticket search results

Adds a link to the scp/tickets.php page (Tickets) allowing for the export of
the data to CSV file. This is preliminary and still needs a few items:
  * An icon + button CSS definition
  * Support for alternate columns (staff assigned, etc.)

Also add beginnings of complex export support (PDF, JSON  and other
formats
to follow). CSV is fully supported for now.

And for brevity, add a Http::download method to allow for consistent and
browser-independent forced page content downloads

Add a %ticket_history table to track ticket states over time, correlated to
the user account changing the ticket. Then, tickets are tracked to the table
when (re)opened, closed, overdue, transferred and assigned.