Upgrade Windows Phone 7 apps to to Windows Phone 8 apps

The development environment for Windows Phone 8 app is better than that for Windows Phone 7 app though the seemingly abandoning Silverlight is still very puzzling.

• Use VS 2012
• Install Windows Phone 8 SDK. 
• Read artilce How to upgrade an app project to Windows Phone 8
• All service references need to be either updated or recreated.
• Install OData Client Tools for Windows Phone Apps if OData is used.
• If WCF data services is needed in a project which does not have a WCF data servcie reference (e.g. using a data service referenced in a library). references WCF data services (Microsoft.Data.Services.Client.WP80, Microsoft.Data.OData.WP71, Microsoft.Data.Edm.WP71) need to be added to the project.  The easiest way to do it is adding a data service reference which automatically add all required references, and deleting it afterwards.
• When publishing the Windows Phone 8 version of a app, use "Add new" instead of "Update selected" on the "Upload XAP" page so the app will be available for both Windows Phone 7 and Windows Phone 8. If "Update selected" is used, Windows Phone 7 version will be  replaced, and the app will not be available for Windows Phone 7 anymore.