Due to problems with the javascript conversion in the website
quickstart, remove the `has_letters` setting to simplify generating
`attrs` for the default `tok2vec`.
Additionally reduce `PREFIX` as in the trained pipelines.
- As much as I dislike YAML, it seemed like a better format here because it allows us to add comments if we want to explain the different recommendations
- Don't include the generated JS in the repo by default and build it on the fly when running or deploying the site. This ensures it's always up to date.
- Simplify jinja_to_js script and use fewer dependencies
