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
Move right sidebar above article for tablet view
Override "en-US/docs/Web/" -style headings in the wiki
Merge
fix bug 911374 - Change case when search box has a value
Move zone images to DIVs to stylable by zone leaders
Set crumb arrows on pseudo-elements for easier RTL support
Make wiki error lists display better
Merge pull request #1326 from darkwing/redesign-tablet-wiki-sidebar

Move right sidebar above article for tablet view
Merge pull request #1334 from darkwing/redesign-search-case-911374

fix bug 911374 - Change case when search box has a value
Merge pull request #1335 from darkwing/zone-image-css

Move zone images to DIVs to stylable by zone leaders
Merge pull request #1336 from darkwing/redesign-crumb-icons

Set crumb arrows on pseudo-elements for easier RTL support
Merge pull request #1337 from darkwing/redesign-kumascript-error-list

Make wiki error lists display better
First structural adjustments for RTL layouts
Merge pull request #1331 from darkwing/redesign-sphinx

Update sphinx settings with redesign
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