[ZWeb] show_subtopics turned off in zope3 wiki

[Simon Michael]

PS note the page hierarchy is still there, it can be seen above the page 
title and when you click "all pages in this wiki", and it is a useful tool 
to divide & conquer and organize our content.

This will happen mostly automatically as you create pages. When you want to 
clean up or reorganize, use the reparent form (at the bottom of each page, 
or in the backlinks view). Try #zwiki for quick help when needed.