Add XW_Extension_Permissions.h and XW_Extension_Runtime.h

This defines two internal interfaces in Crosswalk to enforce
permission control for extension API and get varibles for runtime.

Also XW_Extension_SyncMessage.h is updated with that in crosswalk
Merge pull request #253 from xuzhang/extension_update

Add XW_Extension_Permissions.h and XW_Extension_Runtime.h
[Application] Add Applicatin extension skeleton and getAppInfo/getAppsInfo support

The implementation is based on spec:
https://developer.tizen.org/dev-guide/2.2.0/org.tizen.web.device.apireference/tizen/application.html

The ApplicationInformation class will fetch an application's information by using
pkgmgr-info/pkgmgr APIs. An internal PkgMgrHandle class is implemented to abstract
appinfo and pkginfo handles.

To get current application ID, we use the Crosswalk app ID from Runtime interface
and translate it to Tizen ApplicationId when application extension is instantiated.
[Application] Add Application API example for getAppInfo/getAppsInfo

Application API needs to be run in an installed app context, so a manifest file
is also added.