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

The client and scp config ajax request only contain the settings for the
multi-file upload widget. So it doesn't need to be fetched unless the widget
exists on the page

Remove default max limit - no size limit is assumed.

Add overlay & loading spinner to client interface - shown on form submission to help cut down on double submits.