Fix cases where first item added via addSubMenu got deleted.

Move ticket status change to unified backend.

Messages are extracted on post-action redirect.

Crowdin recreates YAML files with indent specifications which Spyc does not
currently handle:

body: |2
  body contents written
  here with 2 leading spaces

This is part of the Yaml spec after 1.0

backportme

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.

Remove retired navigation background image

Names parsed from incoming emails are stored in the database as is. This
pull request addresses potential XSS vulnerability due to improper display
of unsanitized names. Going forward names will be scrubbed on create.

  * Paper sizes
  * More prompts on ticket filters

References:
(Crowdin login required)
http://i18n.osticket.com/translate/osticket-official/148/enus-de#4407
http://i18n.osticket.com/translate/osticket-official/148/enus-de#2379

The software defines at least three contexts for the phrase "Open"

  * The name of a ticket queue (Open tickets)
  * A status of a ticket (Open / Closed)
  * An action to be performed (Open a ticket)

References:
(Crowdin login required)
http://i18n.osticket.com/translate/osticket-official/148/enus-de#2915

Fixes #145

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