[UX] Provide options-element-like UI for the "Style List" text area for text formats

In the text format configuration area, We have a single giant text area for providing allowed CSS classes and their human-readable labels:

The description text for this textarea is as follows: A list of classes that will be provided in the "Styles" dropdown. Enter one class on each line in the format: element.class|Label. Example: h1.title|Title. Each style should be in your theme's main CSS as well as in your theme's ckeditor-iframe.css file.

Though it's possible to read all that text and get the data entered into here correctly, we could make it a lot easier on our admins if we provided a key/value entry system like we do for field values.

We might even be able to use an options-element since both text areas use the vertical pipe as separator.