Set noLegacyStyle: true and adjust structure accordingly

See http://www.w3.org/respec/ref.html#nolegacystyle for documentation.

Highlights:
* No auto-generated sections for attributes and methods, so less noise in the ToC and further down.
* The generated sections were sorted alphabetically so often differed from the WebIDL ordering, which is confusing. The hand coded markup is not re-ordered.