Also, default size should not decrease if different signatures are selected

Previously the richtext editor introduced the loss of the collision
avoidance feature.

  * Upgrade to Redactor 9.1.7
  * Use a (x) icon from font-awesome for the dialog

Previously, deleting a draft either from a form [reset] button or from the
trashcan would delete the draft and cancel the draft system for the
remainder of the page's lifetime. This patch deletes the current draft and
resets the Redactor's content, but then it starts a new draft cycle so
drafts can be continued. It also prevents posting to an undefined URL if the
draft_id has not yet been setup.

Fixes #90

Fixes #65

If the [reset] button refreshes the page, ensure the draft deletion is
completed before the refresh is performed or the draft deletion will be
canceled.

The issue has been filed with Imperavi, but no ticket number or other
tracking information was returned.

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