Add PublicKeyToken, StrongName and Identity to EnvDTE.Reference

Used by Entity Framework 6
Fix error when installing EF.SharpDevelop NuGet package.

Enumerating the EnvDTE.Project.Object.References in a different app domain
was trying to load the PackageManagement assembly and failing. Changed
EnvDTE.References so it only exposes types in the SharpDevelop.EnvDTE assembly
and switch to using IEnumerable on the EnvDTE.References class.