Drupal name and links still referenced throughout

[laryn]

It looks like there are Drupal references and links in a variety of places in this module yet.

e.g.

Nodes are a Drupal site's primary content.

[herbdool]

I've made a pass of updating this. I left in links to the handbook because there's no replacement yet. And to specific d.org issues so we know why a decision was made.