This addresses cases where incoming emails doesn't include charset and
mailbox may include non-ascii characters.

function splitHeaders updated in order to correctly parse mail header lines
starting with tabs

Signals added:
  * mail.received
    Called after the mail is received into the system and before it is
    processed by the mail system. This signal is useful to do header
    injection. Raw message/rfc822 included in 'raw' key in the info

  * mail.decoded
    Called after the initial decoding of the message. The header and bodies
    are broken out, however, Unicode decoded may not have been performed
    yet. This signal is useful to affect the interpretation of the message,
    such as TNEF processing, etc.

  * mail.processed
    Called after all internal processing is completed. All Unicode
    processing is complete, bounce detection and other mechanisms have
    completed. This signal is useful to do things like attachment scanning
    or content filtering.

Otherwise, if a decoded email name has a comma in it, for instance

From: =?utf-8?B?RnJ5ZGVubHVuZCBIeW3DuGxsZXIsIEJldHRpbmE=?=
    <bettina.frydenlundhymoller@domain.com>

The address list will be parsed incorrectly since the comma has an ambiguous
significance. Usually, the personal name would be quoted; however, since it
is encoded, there is no need to quote it.

Sometimes an MTA may just send back the headers of the original message
rather than the entire original message. Such an email will have a
`text/rfc822-headers` part which will be the complete headers of the
original message.

Without this patch, osTicket will create a new ticket for the bounce message
rather than attaching the new internal note to the existing ticket.

References:
https://tools.ietf.org/html/rfc1892

Such images are attached to emails by Lotus Notes. Technically, these images
are valid attachments, although historically osTicket would reject them

email.

This is necessary to eliminate possible loop when an email is sent to a
virtual/aliased address. Not all mail servers add delivered-to header!

If a non-text attachment specifies a charset in the content-type header,
don't transcode the content before saving it to the database. This can
corrupt attachments which have a header like the following:

Content-Type: application/pdf; charset=UTF-8

Since a PDF contains binary data, coercing it to UTF-8 encoding will drop
characters not valid in UTF-8 and will corrupt the attachment data.

This is necessary so we don't add delivered-to addresses to the list of
addressee/collaborators.

Previously, the Delivered-To header was only used if the To header was not
found

If a wrapped mail is sent, copy the Delivered-To header into the nested
message so it will be clear(er) how the mail arrived into the system. Also,
copy the Message-Id into the nested mail if there is none to help against
mails delivered repeatedly.

If an email arrives at the system and the system cannot determine why the
mail arrived (ie. a system email was not found in the To or Cc headers), the
recipients list should be maintained.

This is useful for generating collaborator lists as well as filtering by the
To and Cc (Addressee) headers.

07fec4c4 introduced the ability to receive
and process messages forwarded as a message/rfc822. However, the email
headers that were saved on file in the %email_info_table were the headers of
the outer message.

This patch pulls the headers from the wrapped message to be saved in the
database. This mainly addresses the email References and In-Reply-To headers
for the email responses from the system.

This would in theory allow us to decide at the email level the content type
to accept.

Fixes a few E_NOTICE messages
Drops bounce checking inside autoReply checking

Best version of https://github.com/osTicket/osTicket-1.8/pull/348

static keyword added to enable strict test mode.

Previously, if a message had a Content-Disposition header, then it could not
be considered as the body of the message.

If the mail received into the system has a content type of 'message/rfc822',
then unwrap the inner message and use it as the parsed email. Effectively,
assume the email was forwarded as an message/rfc822 attachment.

Previously, the mail parsing and fetching system would recurse unbounded
searching for bodies by content-type

Provide facility to set collaborator status on add.