Settings for storage backend and general max size setting for agents

Allow fields to be configured for view / edit / required for both agents and
end users. Fields can also be disabled now so that the field remains in the
form but is no longer displayed for new entries.

Allow tickets to be created without a subject — use the help topic full name
instead.

Only cache results for ALL items

And fixup the migration patch

Help topics and filters can override the default status

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.

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

- 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.

Client accounts now that the user is verified either via staff or the
client's email mailbox, there's a much lower risk to showing a verified user
other tickets and virtually no reason that an administrator should have to
turn the feature on.

  * Administrator can disable the new activity alert
  * Administrator can disable automatic collaborators from email headers

Administrators can disable client edits of ticket information. Hopefully,
this will eventually be replaced by role-based ACLs placed on individual
forms and fields.

  * Include a `bk` column to store the storage backend
  * Include a `signature` column which represents a repeatable hash of the
    file contents
  * Rename `hash` to `key` since it isn't a real hash

If a ticket is currently unassigned and your respond to it, it's yours. If a
ticket is closed and later reopened due to a new message, the last
respondent will always be assigned if available at the time.

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

Make sure ticket api controller enforces attachments settings (don't trust data parsers).

* Collapse date settings into system settings.
* Move auto-cron setting to emails settings page.
* Move clickable urls setting to tickets settings page.