Previously, the display of the button was incorrect and more than one button
might have been displayed.

htmLawed stripped/discarded <div> tags nested inside inline tags such as
<a>. The previous replacement engine would replace <img> tags with <div>
tags and would cause the HTML to be corrupted by htmLawed.

This patch uses <span> tags which have CSS rules to be displayed as
inline-blocks. This should stay truer to the normal sizing and placement of
the original <img> tag.

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

Since the ticket thread is nested in a div now (required for inline videos
to be displayed correctly), the image hover caused the images to be shown at
the end of the thread entry body rather that its original location.