bfsc: Add children-nav partial

Create an <ul> with references to children pages
bfsc: Add vnav page template

Attention: This is only for "children", not
"one level below root in the current rootline"
bfsc: Change Examples page's template
bfsc: Add stubs for Examples subpages
bfsc: Add images: Fried exceprt from 7-1
bfsc: Test: add image to Home page
bfsc: Set up page layout with vnav (WIP)

THis is still awful, but at least it allows to work on the page content.
bfsc: Rename challenges (path) to examples/house-style
bfsc: Rename paths to examples subpages

make them plural
bfsc: Major review of Examples page

In particular, take into account that there now are actual subpages
available.
bfsc: Add initial text for Style Examples
bfsc: Initial text for Examples/House Styles
bfsc: Small touch on Examples/Styles
bfsc: Finish _text_ on Examples/House styles

Note that the examples themselves are still lacking