s/NodeJS/Javascript #211

After some discussion, @daniel-jones-dev has kindly agreed with my idea to refer to our JavaScript client library as "JavaScript", not "NodeJS" - as I believe that more people will be looking for "JavaScript", and anyone who needs server-side JS (as all our JS-loving customers) will understand they can use our JS client library in Node.

Having set this precedent in the revised intro page and Paul's mini guide, I'd like to propagate it throughout the docs.