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/application/PhabricatorApplicationDiffusion.php

@@ -30,6 +30,10 @@ final class PhabricatorApplicationDiffusion extends PhabricatorApplication {
     return celerity_get_resource_uri('/rsrc/image/app/app_diffusion.png');
   }
 
+  public function getHelpURI() {
+    return PhabricatorEnv::getDoclink('article/Diffusion_User_Guide.html');
+  }
+
   public function getRoutes() {
     return array(
       '/r(?P<callsign>[A-Z]+)(?P<commit>[a-z0-9]+)'