Multilanguage Support via gettext

- added gettext encapsulations to all texts i thought necessary
- added fallback function for the case that the gettext extension isn't loaded
- added browser language detection
- added gettext to the list of optional extensions in setup
- rewritten some of the texts to use sprintf instead of appending strings
- added german translation file
- removed mark_overdue-confirm from cannedresponses.inc.php

extend multi language support and a fex fixes

- Better detection of translation files
- Added functionality to redirect language codes (see redirecting
language codes)
- Ticket Status can be translated
- The Datepicker can be translated
- Extended functionality of 'testlang.php' to show what language code is
used to translate

Forgotten to apply a patch from RC5 to RC6

- Forgotten to change $var to $vars in line 380 of class.mailfetch.php
- Removed unneeded comment

Added php_gettext as primary translation engine

- Added php_gettext support (thanks to Danilo Segan and Steven
Armstrong)
- php_gettext is now the primary translation engine
- Extended language detection functionality

Add error/misconfiguration checks and fix undefined variables

Previously, they were displayed in seemingly random order, did not honor
proper nesting, or declared sort order.

On validation errors, `$faq` will be set to something non-null, like
`false`, but will not be an instance of a Faq article.

- Proofread large portion of help tips.
- Implement help tip links in YAML files.
- Fix GUI spacing of some elements.
- Add <label> tags to a few form elements.

Fixes oversize image display to be resized in both the ticket thread and
the redactor editor in (at least)

  * Ticket-view boxes
  * Client new-ticket form
  * Staff new ticket
  * Page add/edit
  * FAQ add/edit
  * Canned response add/edit

Fixes osTicket/osTicket-1.8#247

Fixes #198

Process inline attachments in thread entry and support inline images in
piped emails

Support inline images across the system, with draft support

Migrate to a single attachment table
    That way we don't need a new table for everything we need to attach an
    inline image to (like a signature, for instance)

Add richtext support for internal notes

Implement images on site pages

* Image paste in Redactor
* Make non-local images optional
* Placeholder for non-local images
* Fix local image download hover
* Don't re-attach inline images