Use IGitHubServiceProvider as global provider

Register IGitHubServiceProvider with singleton Service class to use as global provider.

src/GitHub.VisualStudio.16/CompositionServices.cs

@@ -85,23 +85,14 @@ namespace GitHub.VisualStudio
 
             var gitHubServiceProvider = new MyGitHubServiceProvider(compositionContainer);
             compositionContainer.ComposeExportedValue<IGitHubServiceProvider>(gitHubServiceProvider);
+            Services.UnitTestServiceProvider = gitHubServiceProvider; // Use gitHubServiceProvider as global provider 
 
             var loginManager = CreateLoginManager(compositionContainer);
             compositionContainer.ComposeExportedValue<ILoginManager>(loginManager);
 
-            // HACK: Stop ViewLocator from attempting to fetch a global service
-            var viewViewModelFactory = compositionContainer.GetExportedValue<IViewViewModelFactory>();
-            InitializeViewLocator(viewViewModelFactory);
-
             return compositionContainer;
         }
 
-        static void InitializeViewLocator(IViewViewModelFactory viewViewModelFactory)
-        {
-            var factoryProviderFiled = typeof(ViewLocator).GetField("factoryProvider", BindingFlags.Static | BindingFlags.NonPublic);
-            factoryProviderFiled.SetValue(null, viewViewModelFactory);
-        }
-
         static LoginManager CreateLoginManager(CompositionContainer compositionContainer)
         {
             var keychain = compositionContainer.GetExportedValue<IKeychain>();
@@ -192,6 +183,11 @@ namespace GitHub.VisualStudio
 
         public object GetService(Type serviceType)
         {
+            if (serviceType == typeof(IGitHubServiceProvider))
+            {
+                return this;
+            }
+
             return serviceProvider.GetService(serviceType);
         }