Reset field content when building a new form

Use http::build_query instead of inline urlencode

Faq articles should be viewed in the .thread-body div in the client portal
like they are in the staff portal.

Also fix a crash when re-rendering the new ticket by staff page after a
validation error.

Use the cdata field when searching and sorting the ticket listing on the
client side.

Consider current status settings to determine if a ticket is reopen-able
Show a warning on staff's ticket view if the ticket is not reopen-able

This is necessary to avoid confusion vs. closed state.

This will allow for more complex widgets to be added as plugins which
include css and javascript media files without manually adding header or
footer lines.

Add context to ticket state name (noun) and action (verbs)

Conflicts:

	include/class.forms.php

Previously, if the enduser registration mode were set to something other
than `public`, the agent sign-in link would not be shown. Now, the agent
sign-in link is always shown on the enduser sign-in page.

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.

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

This requires a hidden setting for the system language or the language
selection of the client (also currently hidden).