Add plugin concept and plugin management system

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

Collaboration -- YAY!! This has to be like the most requested feature ever!

Happily-Reviewed-By-But-Not-Certified-By: Jared Hancock <jared@osticket.com>

Conflicts:
	include/ajax.users.php

And add fixup rebase conflicts, and add nice page for unconfigurable plugins

Like HTTP authentication

This includes the initial concept of pluggable authentication along with the
initial concept for a plugin management system.

Change fromForm routine takes the actual form and do validation and call
fromVars with clean data

Add fromVars to do the actual user creation (previously named fromForm.

Include all validation erors

tips: Auto-flip pop-over and fix a few typos

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

User lookup revisited

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

Include all validation erors

Conflicts:
	include/ajax.forms.php
	include/ajax.tickets.php
	include/class.user.php
	include/staff/ticket-view.inc.php