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/files/controller/PhabricatorFileListController.php

@@ -177,7 +177,6 @@ final class PhabricatorFileListController extends PhabricatorFileController {
       $side_nav,
       array(
         'title' => 'Files',
-        'tab'   => 'files',
       ));
   }
 

src/applications/files/controller/PhabricatorFileMacroListController.php

@@ -158,7 +158,6 @@ final class PhabricatorFileMacroListController
       $side_nav,
       array(
         'title' => 'Image Macros',
-        'tab'   => 'macros',
       ));
   }
 }