Issue 3785: Web:Examples: Enclose in box

Issue 3785: Web:Examples: Enclose in box

I think the pages below Introduction (and probably Community too)
should consistently start with a box and a subheading,
because there is no eye-catching page heading.

This is _one_ option to do that for the Examples page.
Others would be:

- Make that @div only enclose the introductory paragraph
- enclose the introductory paragraph _and_
  - add a headingless div around the examples _or_
  - add a div with @subheading "Gallery"