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/paste/controller/PhabricatorPasteViewController.php

@@ -122,7 +122,6 @@ final class PhabricatorPasteViewController extends PhabricatorPasteController {
       ),
       array(
         'title' => 'Paste: '.nonempty($paste->getTitle(), 'P'.$paste->getID()),
-        'tab' => 'view',
       ));
   }