This is safe now, because the title is appropriately encoded in
class.thread.php/ThreadEntry::create()

Fixes #567, #718

Incoming messages with empty body and an inline attachment might not have
parts - depending on encoding used.

* Use "-" tag for emails with empty body/message

Add SLA to ticket info table.
Move subject to the top of ticket thread.

 - Add To: address
 - Add ability to diable emailed replies
* Post Note
 - Make note title optional.
 - Add additional ticket status (state) options.
* Assign
 - Add claim to dropdown for self-assignments.

Use the new dialog popup to confirm express actions above.
Convert the fileformat to unix

fixing padding on ticket info table and changing mroe button to trigger dropdown on the entire button

Add print options supports - staff can now print a ticket thread without internal notes + select paper size on the fly

Add Team::hasMember utility method to assist in determining if a ticket is
owned by a team that he currently-logged-in-staff is a member of. Then,
check if the ticket is assigned to a staff member other than the current
staff or to a team that the current staff is not a member of. If so (the
ticket is not assigned to the current staff), then display the warning
banner showing who currently owns the ticket.

Protect againts cross-site request forgery attacks by requiring a special
form-field or header to be sent with requests that modify ticket system
data.

This meant a slight change to the AJAX ticket locking mechanism. It was
defined to lock with a GET request; however, GET requests are defined as
safe methods and should not modify backend data (such as a lock
acquisition). Therefore, the the lock acquire AJAX method was changed to
require a POST method.

Also remove old, no-longer-used staff panel include files

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.