Fixes #772

If a ticket has a due date and does not have an SLA set, the ticket would
never transition to overdue. This patch addresses an SQL flaw preventing the
ticket from being transitioned.

Fixes #757

This patch affords an administrator the ability to remove the
[#%{ticket.number}] from the email template subject line for the new ticket
autoresponse and the new message autoresponse. Previously, the ticket number
with a prefixed hash in brackets was used to identify which ticket thread an
email was in reference to.

With this patch, the email message-id (which was already kept on file) is
sent in the MIME "References" header. When a user responds to and
autoresponse email, the "References" will include this message-id in the
return email. The ticket thread is then matched up with the email based on
the message-id rather than the subject line.

Ticket numbers are still supported in the subject line, in the event that
non-compliant email clients do not properly include the References header.

SLAs can be marked transient. When a ticket is assigned to a transient SLA
and it is transferred to a department or help topic having a default SLA,
the SLA will change to the SLA of the new department or help topic. This
process can continue as long as the ticket has a transient SLA assigned.
Once a non-transient SLA is assigned to the ticket, the SLA will no longer
change automatically. Thereafter, the SLA can only be manually changed.

Spelling, grammar and readability in upgrader documents
  - Tweaked spelling, grammar and wording to make the text of the upgrader
    pages more readable.
Fixed spelling regression
  - Higly —> Highly
Spelling and readability fixes for /include/class.* files
  - Fixed some spelling mistakes
A couple more spelling/readability fixes.
  - More fixes

When creating tickets, ensure that data which should not contain leading or
trailing whitespace is trimmed and validated accordingly

Change the config table from a column-based table to a key-value table
with namespacing. This allows several parts of osTicket to store their
respective configurations in the same table without requiring database
structure updates

'namespace' is reserved in PHP

Remove SLA when overdue flag is cleared AND est. duedate is in the past. Only managers can manually clear overdue tickets.

Fix minor spacing/formatting issues.

 -> Open - only contains unasssined tickets if 'show assigned tickets' is off.

Set SLA on transfer *ONLY* when a ticket doesn't have one. Overwriting manually set SLA is the concern here...

Add methods to get estimated duedate and sla duedate

Add routine to import emailed & api files

Log internal note on mass close/reopen - instead of activity log.
Default to 'SYSTEM' if note poster is not passed.

Make sure SLA plan is 'active' when marking tickets overdue.