HTML ticket thread, inline images and draft support

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
Changes made after feature review
Fix non-local images on client interface
Revise initial email templates

Ticket notice and ticket auto-reply should not be formatted inside a table
since the %{message} or %{response} should be allowed to flow freely in the
email rather than be crammed inside the table.
Fix html2text output for empty headline elements
Fix attachment data on new install
Allow semicolons in single quotes in schema files
Fix upgrade from 1.8 develop branch
Enable attachments by default
Fix canned response injection
Don't handle text email messages like HTML

This patch changes the behavior of the mailer to support a 'text' option to
hint if the message is a text-only message. If so, no HTML processing will
be performed on the message and a text-only email (with no inline
attachments) will be emitted and sent.
Merge pull request #5 from greezybacon/feature/html-thread

HTML ticket thread, inline images and draft support

Reviewed-By: Peter Rotich <peter@osticket.com>