Remove all code referencing old tab navigation

Summary:
  - Add getHelpURI() to PhabricatorApplication for application user guides.
  - Add a new "help" icon menu item and skeletal Diviner application.
  - Move help tabs to Applications where they exist, document the other ones that don't exist yet.
  - Grep for all tab-related stuff and delete it.

Test Plan: Clicked "help" for some apps. Clicked around randomly in a bunch of other apps.

Reviewers: btrahan, vrana

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D3267

src/applications/conduit/controller/PhabricatorConduitController.php

@@ -25,21 +25,12 @@ abstract class PhabricatorConduitController extends PhabricatorController {
   protected $showSideNav;
 
   public function buildStandardPageResponse($view, array $data) {
-    $doclink = PhabricatorEnv::getDoclink(
-      'article/Conduit_Technical_Documentation.html'
-      );
-
     $page = $this->buildStandardPageView();
 
     $page->setApplicationName('Conduit');
     $page->setBaseURI('/conduit/');
     $page->setTitle(idx($data, 'title'));
     $page->setGlyph("\xE2\x87\xB5");
-    $page->setTabs(array(
-      'help' => array(
-        'href' => $doclink,
-        'name' => 'Help')
-      ), null);
 
     if ($this->showSideNav()) {