Special:MobileWebApp and Special:Manifests

Introduce a new special page with AppCached HTML
(CSS and JavaScript is not appcached... yet)

* Update JavaScript modules to support an app mode
* Only run header-loaded event if mw present (not present with no
internet)

Heavily based on work by Adam Baso

Change-Id: Ifc9c405766f5a95d1a97d36808ecf5992901a80b
Merge "Special:MobileWebApp and Special:Manifests"