To conform to documentation best practices add structure
to the home page (via the Diataxis framework). A Sphinx
extension is used to display panels.
The Release notes quadrant/panel will become the Reference
section once there is material to put there. The Release
notes will then fall under the Project hierarchy.
Add custom CSS to make the above panels respect the page's
text width.
Resurrect the search facility in a more direct manner.
Move the code of conduct reference to the home page.
Change-Id: I963d5f5b3e81b021747c0050fedd208e68ab920e
1fa01acd73