Implements rich text editor widgets. Unlike most widget types, the rich text editor does not use a modal; instead you edit in context on the page.
Return just the rich text of the widget, which may be undefined or null if it has not yet been edited
TODO We may want to use the default widget load, if we start having nested areas in rich text widgets to support lockups
Rich text editor content is found in the div itself as markup, so don't redundantly represent it as a data attribute.