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/diffusion/controller/DiffusionController.php

@@ -47,15 +47,6 @@ abstract class DiffusionController extends PhabricatorController {
     $page->setBaseURI('/diffusion/');
     $page->setTitle(idx($data, 'title'));
     $page->setGlyph("\xE2\x89\x88");
-    $page->setTabs(
-      array(
-        'help' => array(
-          'href' => PhabricatorEnv::getDoclink(
-            'article/Diffusion_User_Guide.html'),
-          'name' => 'Help',
-        ),
-      ),
-      null);
     $page->setSearchDefaultScope(PhabricatorSearchScope::SCOPE_COMMITS);
 
     $page->appendChild($view);