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

As suggested by: https://github.com/osTicket/osTicket-1.8/issues/755

This will simplify where PJAX needs to be disabled by simply including the
navigation as part of the PJAX response.

And extend the information to email templates

*This is a major redesign / rework of the osTicket base*

This patch drops the concept of static ticket metadata and allows for an
admin-configurable arbitrary data that is attachable to tickets

The system is architected such that the base osTicket install now comes with
a "default" form that has fields for subject, name, email, and phone number.
This form is editable to allow for the addition of arbitrary other fields;
however, the basic fields must remain in order to be associated with a
help-topic and attached to a ticket.

This concept can be expanded to allow for arbitrary data associated with
registered clients or ticket thread items.

Forms are comprised of sections. Sections have a title and instructions
properties and a list of fields. Fields have various implementations to
represent different data such as text, long answer, phone number, datetime,
yes/no, and selections, and are configurable to define the look and feel and
interpretation of the respective form field.

Dropdown lists are represented as "Dynamic Lists", which are
admin-configurable lists of items. Dropdowns can be optionally represented
as Bootstrap typeahead fields.

This also adds the start of a simple ORM which will hopefully be expanded in
the future to support multiple database platforms. Currently, only MySQL is
implemented.

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

Use minimized version of css.

Change header to match the new names