Break out rich text area into separate plugin

[jadefish]

The rich text area component should be its own plugin.

Rationale

The rich text area component:

1. depends on an external JS library (Quill)
2. was developed before plugins existed
3. is more configurable than the POM abstraction layer comfortably allows
4. should be substitutable for other rich text editing JS libraries

The rich text area as a built-in component doesn't support points 3 and 4 above.