Also, give a "Browser not supported" error for browsers which do not support
the Blob constructor.

This script adds a single download script, 'file.php', which provides access
to files of all types to all users. It uses a HMAC signature system with an
expires time, which allows signed URLs to be sent to external users.

This also fixes an issue with the Http::cacheable() method, where the
last-modified and Etag headers were not properly compared, which resulted in
permanent cache misses by the client.

  * Use the title of "Information" with internal tag of "info"
  * Add "Visibility" column to UI and retire "Required" and "Internal"
    columns
  * Add visibility selection to new fields and show visibility to the user
    information fields when displayed on the ticket details form
  * Make the visibility settings translatable
  * Use constants internally for visibility configuration detection
  * Use a larger input when managing the information HTML content
  * Fix validation errors for new fields
    * Enforce new field name uniqueness
    * Enforce new field name character validation

The staff portal has a feature where the date fields are converted to
YYYY-MM-DD prior to form submission. However, this code was not ported to
the client portal. Therefore, for non-US date formats (d/m/Y for instance)
would not be processed properly by the server and would be nulled prior to
validation.

Only one file is supported at a time now; but at least the files are saved
and displayed in the event of validation errors.

On some setups, IE v10 on Windows 7 at least, text added to the Redactor
editor after an image is inserted (via the image popup dialog for instance),
will not be retrieved via the ::get() method and so will not be submitted
with the form submit button.

This patch introduces a workaround by manually calling ::sync() for the
Redactor when the submit button is pressed — just before the form is
submitted.

Also add a drop-down list of common links include ticket links and login
pages for both agents and end users.

And add translations for the draft mechanism