Refactor our npm scripts

OK, so currently, I find it quite annoying that

1. I need to open 2 separate cmds to do local development (one with bundle exec jekyll watch and another one with npm run watch)
2. Most importantly, I feel like our scripts don't include important parts.

When I do npm run css it makes sense to me to run the docs-css script too, and so on.

Opening the issue to track it and to find solutions to improve this.

/CC @Johann-S @bardiharborow