Bug 1005818 - Part 1: Load a widget as an app if the |src| is in the |widgetPages|. r=fabrice, sr=sicking

1. Add permission |embed-widgets| and Element attribute |mozwidget|
2. Add |hasWidgetPage| in /mozIApplication.idl
3. Check permission |embed-widgets| and the |src| is in the |widgetPages| when |GetAppManifest|
4. Add test case
5. Should enable preference |dom.enable_widgets|
Bug 1005818 - Part 2: Only limited browser API are available to a widget. r=kanru

1. Add |ownerIsWidget| in nsIFrameLoader.idl
2. Add |GetReallyIsWidget| in nsIMozBrowserFrame.idl
3. Hide the methods of browser API of a widget
4. Hide security-sensitive mozbrowser events of a widget