Previously the American date format (m/d/Y) was used exclusively for
formatting dates in the datepicker widget. This patch enables the widget to
be formatted based on the format set in the admin panel.

Fixes #829

If a Content-Disposition header exists for an attachments, it isn't required
to have any parameters (like a file name)

Overhaul the popup tips from the installer to make them translatable and
work toward popovers for all the admin and staff panel settings.

Also remove CSS properties from the style attribute that are browser
specific (like -webkit-* and such)

Previously, clients would not be able to create tickets if an internal,
required field existed on any of the forms presented to the user. Instead,
they would be stuck at permanent validation failure because there was no
data for a required field not shown.

This patch adds a feature to the form and dynamicFormEntry objects'
isValid() method to receive a callable to filter which fields' errors should
be added to the form's errors list. This allows for more complex validation
where in some cases, validation errors should not be considered on some
fields.

Fixes #45

Fixes #40

Move the cacheable code to the Http class and allow the client configuration
to be cached in the browser

Which will help fight off spammers. This should be coupled with logic that
will add some enticing fields, like 'email' and 'name' to invite bot input.
Then, on the form processing side, a spam submission can be detected and
handled differently from human submissions. This should lessen reliance on
CAPTCHA only as spam detection.

Previous the options defined for the Mailer::send() function were confusing
when sending an In-Reply-To header

Previously, the References header emitted by the system for new thread
entry auto-responses and alerts included the message-id for which the email
was a reply in the `References` header. This patch corrects the issue by
placing the reply message-id in the In-Reply-To header, and constructs a
correct References header.

That is, if available, the References header received in the email that was
used to create the thread entry is appended to the message-id the email is
actually in reply to. This is the expected usage of the References header.

in Client::getLastTicketIdByEmail()

This provides better compatibility with mPDF, which doesn't support the CSS
white-space:pre-wrap property

Previously, the value of the selection was lost in the request and, if the
form field was marked as required, then a ticket could never be submitted.

Use a PHP setup which uses the built-in PHP tokenizer to parse and traverse
PHP scripts to determine (possible) access to uninitialized variables

Also, add footnotes to the bottom of the rendered document for links that
are longer than half the document width.

Fix preg_replace bugs

* %{ticket.thread.original} represents the original message submitted when
    creating the ticket
* %{ticket.thread.lastmessage} represents the most recent message submitted
    by the end user

If the xml extension for php is not loaded, this patch will do a better job
of honoring line break hints in the html.

Provide fallback html2text mechanism if PHP xml extension is not available

Allow for type and encoding specification of the message body and better
describe the integration with custom form fields.