* Edits to the "Angular Modules (NgModule)" page (ngmodule.jade). In order to fix some broken links, I defined their destinations in forms.jade and pipes.jade.
* Changed "Angular module" to "NgModule" and other edits.
- I assumed that the “Angular Module FAQs” cookbook page should change to “NgModule FAQs”, so I updated that page as well.
- I updated the name in page headers, TOC titles, and links on the Docs Home page (index.html).
- I noticed the Advanced and Cookbook sections are organized alphabetically, so I reordered the pages and references to reflect that.
* docs: adjust page heading levels
Only the page TOC should be at heading level 1. All other headings
should start at level 2. This commit also removes duplicate headings,
in continuation of #2796.
(This fix is necessary to support an auto-TOC feature.)
