CB-5109 - Windows 8 and 8.1 - InAppBrowser implementation

In Windows 8.1, there is a new WebView control.
It can be used to create an InAppBrowser implementation.

http://msdn.microsoft.com/en-us/library/windows/apps/dn301831.aspx

In order to meet the new ambitions about Windows code reunification, I centralized the Windows 8 and 8.1 version Inside the same proxy (located in src/windows/InAppBrowserProxy.js).