Show different messages and placeholder on ticket(s) deletions

Move ticket status change to unified backend.

Also add a drop-down list of common links include ticket links and login
pages for both agents and end users.

Ticket numbers are now configurable as a system-default and by help topic.
Previously, an administrator could select between six-digit random and
sequential numbers. Now, the sequence is selectable so multiple sequences
as needed, and a format can be specified to define how the ticket numbers
look. Formats can also be defined for each help topic.

Add an interface for custom list items.
Implement CustomListItem for built-in and custom lists.

Add original and last message quotes to canned responses

Show user search box when adding a new user

Support adding remote user to an organization

Support adding existing or new users while on organization page.

And deadband session token updates to 1 per 30 seconds

And install initial data in target language. Also configure help tip
popovers to be in the configured, default system language.

Ensure aquireLock doesn't interfere with renew/release

Requires authentication plugins to implement a new AuthDirectorySearch
interface to define the two functions

Previously, the user information could only be modified on the ticket-view
page. For instance, if creating a new ticket for a user, no new information
could be added or modified on the user until after the ticket was created

Fixes osTicket/osTicket-1.8#281

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