This patch adds an error to the page if unable to configure the archive
folder and POP was selected as the mailbox protocol. Generally, POP servers
do not support anything but the INBOX

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.

Here's an example email structure:
```
multipart/mixed
 - multipart/report; delivery-status
   - multipart/alternative
     - text/plain
     - text/html
   - message/delivery-status
   - message/rfc822
```

The previous code would only find the body if the email main headers had:
Content-Type: multipart/report; report-type="delivery-status". In such a
case it would scan for a plain/text body.

This patch will scan for the usual body if the scan for the body as usual if
the report scan did not find anything.

Also, output errors to stderr when running API from the command line

It seems that most systems handle the newline character alone without a
problem; however, some systems cannot handle the standard CRLF line ending
at all.

The %ticket_email_info table needs an index on thread_id. This is done in
the `develop-next` branch; however, this patch helps alleviate performance
issues on the main branch until the `develop-next` branch is collapsed for
main line development.

Fixed typo

This also adjusts the logic internally to lookup the priority by the
priority_urgency field, which should be constrained to follow priority
precedence over the priority_id field.

Because CSV has no way of indicating a content character set, writing the
file with a Unicode byte-order mark is useful to declare the content in
UTF-8 encoding.

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.

This will help when saving rules with trailing spaces for instance, which
may make things not match when visually the administrator would otherwise
expect the filter to match.

Fixes #1834

For a yet unknown reason, the association between the field implementations
and the DynamicFormEntry object is not maintained from calls to
DynamicFormEntry::getFields().

This patch addresses the issue by always associating the "form" when
returning from ::getFields()