email: Fix possible crash if no body in email

Reviewed-By: Peter Rotich <peter@osticket.com>

Fix possible crash if `i18n` folder is not readable

Reviewed-By: Peter Rotich <peter@osticket.com>

Plus-addressing test

Reviewed-By: Jared Hancock <jared@osticket.com>

Conflicts:
	WHATSNEW.md

Conflicts:
	include/class.mailparse.php

Conflicts:
	include/staff/templates/user-lookup.tmpl.php

lint: Fail on js syntax errors

Reviewed-By: Peter Rotich <peter@osticket.com>

mysqli: Allow for persistent database spec

Reviewed-By: Peter Rotich <peter@osticket.com>

Allow disabling the collaborator features

Reviewed-By: Peter Rotich <peter@osticket.com>

  * Administrator can disable the new activity alert
  * Administrator can disable automatic collaborators from email headers

Use `p:` in the database hostname specification, so `p:localhost` for
instance. This will help with SSL and remote database users.

References:
http://www.php.net/manual/en/mysqli.persistconns.php

The warning was meant to be humorous but apparently the world has no sense
of humor.

Stop propagation on intercept

Credit: http://stackoverflow.com/a/7385673/2867073

It was also the last-modified date of the category -- not the actual FAQ
article itself

When checking ticket access - only consider assignment IF the ticket is
open. This is required since staff_id field is overloaded to show who closed
the ticket.

This can happen when associated department is private and the system has no
default department (which is possible with v1.6 upgrade)