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

This is necessary for some mail clients which indicate encoding in GB2312
but actually use GBK encoding.

This correctly handles a bounce message with the following layout:

multipart/report; report-type=delivery-status
    multipart/alternative; differences=Content-Type
        text/plain; charset="us-ascii"
        text/html; charset="us-ascii"
    message/delivery-status
    message/rfc822

Fixes #1854

Several mail clients do not return the Message-ID header in a In-Reply-To or
References header as they should. The assumption by such mail clients is
that the email be threaded based on the Subject header. However, osTicket
does not require the ticket number to be placed in the Subject header and so
has trouble threading email from such systems. osTicket embeds a copy of the
Message-ID header (or compatible version) in the body of the message in
hopes part of the message will be returned.

Many mail clients (such as osTicket) strip and clean the HTML when
processing HTML email. Previously, the message-id token was embedded in a
@data-mid attribute, which was likely stripped before the HTML email would
be returned back to osTicket.

This patch suggests that the token be placed in a @class attribute, which
has a much better chance of returning to osTicket.

Follow-up PR to the comment here:
https://github.com/osTicket/osTicket-1.8/commit/06d3a0f3e2a4557ca72faa916859b9315635dfe4

Copy+Pasting images from a ticket thread or from a FAQ article to the HTML
editor and submitting will result in the URL *not* being properly rewritten
for storage in the database. When images are uploaded, a relative URL is
returned from the server and embedded in the HTML editor. However, when
images from the system are copy and pasted into the editor, an absolute URL
with the http:// scheme is included. This URL was not properly handled by
the URL rewriter in Format::localizeInlineImages().

This patch addresses the issue by properly handling both relative URLs from
image uploads and absolute URLs from copy and pasting.

Fixes #1926

Also fix bug where bogus charset names like `iso` were confused with valid
charset names starting with that text, such as `iso-8859-2`.

add __() function for not translated words.

Ensure that the References header that is included with outbound email
definitely includes the References header from an email received into the
system, if at all possible.

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.

If an update to an object such as a ticket results in a corresponding update
to the CDATA table, and one or more of the fields have been deleted from the
ticket details form, then, avoid updating the CDATA table for those fields.

This fixes an issue where the CDATA table is dropped and recreated when
fields are added and removed from the form. The table will only contain
fields which are currently on the form when the table is created. Therefore,
deleted fields will never be on the CDATA table and will result in an SQL
error.