Linebreaks mode will result in <Enter> key adding a <br/> element to the
HTML markup rather than starting a new paragraph <p> element.

This patch also changes the behavior of the <Tab> key to change focus away
from the Redactor editor rather than indenting the current block.

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