Preserve text formatting on the internal note posted to a new ticket by
staff if HTML thread is disabled.

When the user is not identified by the web interface, such as processing
email to tickets, attempt to locate and include the user filter information
when matching the filter to the new ticket data.

Unassign tickets on transfer when the target department has assignment
restriction and the assigned staff is not a member.

Disable claim (quick self-assignment) when above restriction is in effect.

Add initial concept of activity alert/subscription model to ticket activity.

When sending alerts to agents, consider the setting of the new message alert
configuration.

Reset field content when building a new form

Fixes #1736 - tickets now have their overdue status cleared when it is closed. It uses the inbuilt clearOverdue method to ensure it is done properly, rather than setting isoverdue=0

Also try harder to send a relevant In-Reply-To and References header back
to the client with the email message.

This fixes a slight issue where the team members would never be included on
the new message alert. Now, the system will send to either the assigned
staff member, if any, or the members of the assigned team, again, if any.

If a new ticket is assigned to both an individual agent and a team, do not
send the email alert to the team lead or the team members.

This patch changes the ticket filter system so that it can be recursively
looped to allow for banning and matching on the reply-to address and name.

  * Fix incorrect mapping to user email address
  * Fix early rejecting of tickets — even if a filter earlier in the
    matching filter list had "stop on match" set
  * Fix ::stopOnMatch referring to incorrect db field

The new logic abandons the early rejection logic in ticket create. Instead,
the normal validation is completed as usual. Thereafter, the filter is
initialized and applied to the ticket. Upon rejection, a RejectedException
is thrown by the ::apply() method of the TicketFilter. The Ticket::create()
method will handle the exception and reject the ticket.

This patch adds a ::getAlertEmail() method to the Department class, which
allows administrators to use the department email address (normally for
replies) as the alert email address. If not specified, the system alert
email address is retrieved instead, automatically.

This affects new ticket by staff as well as honoring the influence of ticket
filters on new ticket, where the status may be set to something other than
the system default. Even the system default may be influenced if it were set
to a closed state derivative.

So the concept is simple: the new status should be set using the standard
logic so that the closed_by staff member, date, events, and other
information is set as normally is when a ticket is closed.

This patch suggests a change to the message-id creation process that
includes stamping the receiving user-id (staff or client) along with the
thread-id of the originating notice. This allows detection of threading if
the clinically brain-dead mail client drops all the other header detection
mechanisms, including the tag placed in the email body, on response.

This patch works for both client and agent communication.

Do not reopen closed ticket, if the system can reliably determine that the new message is an
auto-response/reply from the end user.

Take into consideration the auto-response settings when sending out new
ticket by staff notice to the end user.

For fields with `name`s which are the same as other fields on the new ticket
form (such as `time` used with the new ticket by staff form), ensure that
data from the fields outside the main ticket form ("Ticket Details") is not
mingled with fields inside the form.

Since this is only a problem for web requests, and specifically new ticket
by staff requests, this patch only applies the field name to data matching
for non-web requests.

When processing the value of a DynamicFormEntryAnswer, if there is no
database-backed, value, then use the value of the associated field.

Consider current status settings to determine if a ticket is reopen-able
Show a warning on staff's ticket view if the ticket is not reopen-able

This is necessary to avoid confusion vs. closed state.

Also, fix duplicate emails where a user as a collaborator would be sent a
confirmation for their own respective email.

And allow for @context to add context to the bare string literal. For
instance,

    /* @trans, @context "noun" */ 'Open'

Would mark the string 'Open' translatable with context "noun".

Cleanup status change form
Add resolve to ticket ticket view
Use the new status table when checking for overdue

Delete tickets for realz when set to 'deleted' status. This commit will be
partially reverted once data retention plugin is added.