Allow selectable Tone prompts

I really like the UX of this module and the better integration with CKEditor. It *almost* replaces the `ai_ckeditor` module I normally use...with one big exception: the "Improve Tone of Voice".

The really nice feature of the core AI module and it's CKEditor integration (and also the Content Suggestion module) is the ability to assign a vocabulary for a list of "Tone terms" and use the description of each taxonomy term as the AI prompt. This allows the client to define multiple "tones" and switch between them.

For example, building a healthcare website, it's common to have some content for Patients, and other content for healthcare Professionals.

Right now I need to keep ai_ckeditor enabled just so they can continue to use the selectable Tone dropdown, but having two AI buttons is confusing for the client.