Remove retired navigation background image

References:
(Requires Crowdin login)
http://i18n.osticket.com/translate/osticket-official/148/enus-de#3411

And add translations for the draft mechanism

Also add some logic to the POT builder to warn about incorrect arguments to
the __() function and friends as well as warn about _() usage.

References:
(Requires Crowdin account)
http://i18n.osticket.com/translate/osticket-official/148/enus-de#3852

If a list item properties form was unable to be saved (likely due to
validation errors) properties for other list items would not be loaded
correctly (via AJAX) afterwards.

When managing properties of list items

  * 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 terms `%d open|closed tickets` need to be made plural so that the terms
`open` and `closed` can be properly translated.

References:
(Crowdin login required)
http://i18n.osticket.com/translate/osticket-official/148/enus-de#3735

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

Also, the final version of the system will not require the `gettext`
extension for PHP

Use a PHP source file for the translation hash table rather than a
serialized version of the array. This will allow a PHP object cache such as
APC to cache the file and remove the overhead of parsing and unserializing
on each request.

Fixes #145