bug 862080: Tools to define and display zone nav

* (redesign only) Populate quick links sidebar from a "Quick Links"
  section in the current document, or any parent DocumentZone documents

* (redesign only) Hide any "Quick Links" section in the current
  document, since it should get moved into the sidebar

* Helpers to deal with extracting & hiding sections in document content
  (section_extract, zone_section_extract, section_hide)

* Tweak to wiki.content.{extract,replace}Section to ignore the heading
  that defines a section

* Add DocumentZone to admin dashboard, tweak unicode repr

* Tests
Only allow toggling TOC when tablet or smaller
Merge pull request #1339 from darkwing/redesign-toc-toggle

Only allow toggling TOC when tablet or smaller
Move subscribe/unsubscribe to seettings submenu
Minor wiki RTL updates to TOC and crumbs
Merge pull request #1340 from darkwing/redesign-settings-buttons

Move subscribe/unsubscribe to seettings submenu
Merge pull request #1324 from lmorchard/862080-zone-navigation

bug 862080: Tools to define and display zone nav
Merge pull request #1341 from darkwing/redesign-wiki-rtl

Minor wiki RTL updates to TOC and crumbs