Feature: Add a WYSIWYG widget

[hackartisan]

Problem being solved

Exhibit designers can't do everything they need to with the available text widgets

Feature details

In order for curators to design with more control, add a WYSIWYG editor like TinyMCE as a Sir Trevor widget. There was a PR for this, but is was closed pending some requested changes. It would be desirable to have it opt-out by default and have external configuration over the editor controls. Both of which are possible.

PR: https://github.com/projectblacklight/spotlight/pull/2066/files

Acceptance criteria