It's possible to paste an image into a Lexxy instance with `attachments: false` set

[lylo]

Steps to reproduce

1. Copy some HTML including an image from Google Docs (or similar)
2. Paste into Lexxy instance which has attachments: false set

Expected result

The image should not be rendered - it should be removed from the DOM

Actual result

The image is rendered in the editor. If you then persist this ActionText::RichText then the content will save as:

<action-text-attachment content-type="image/*" filename="" width="602" height="316" presentation="gallery" caption="">☒</action-text-attachment>

Subsequently editing the rich text results in a ActionView::MissingTemplate error.

Missing partial app/action_text/attachables/_missing_attachable with {locale: [:en], formats: [:html], variants: [], handlers: [:raw, :erb, :html, :builder, :ruby, :jbuilder]}.