Adding the project file for Windows Universal projects

- DO NOT merge yet
- Created the project to generate the Win8.1+WinPhone 8.1 universal binaries
- The Facebook Authentication for WinPhone 8.1 app works. However, on WP8.0, the SDK relied on elements being present in WMAppManifest.xml. Since in 8.1 this is not present, a new scheme has been designed. It is assumed that a XML file FacebookConfig.xml will be present in the application root folder containing the requisite elements
- The way the redirect back from Facebook app is handled has changed in WP8.1. The app must trap the OnActivated event handler and parse the URI  from IActivatedEventArgs.
- Documentation on the website needs to be updated
- The UI controls - Login, Photo Picker, Place Picker and Friend Picker have not yet been tested on Windows Phone and are  unlikely to work at the moment.