OVR Toolkit Notifications (#751)

* Added OVR Toolkit notification support

* Change order

* Self identify by user-agent.

* Fix comments

Dotnet/AppApi/RegistryPlayerPrefs.cs

@@ -282,7 +282,7 @@ namespace VRCX
 
             var thread = new Thread(() =>
             {
-                using (var openFileDialog = new OpenFileDialog())
+                using (var openFileDialog = new System.Windows.Forms.OpenFileDialog())
                 {
                     openFileDialog.DefaultExt = ".json";
                     openFileDialog.Filter = "JSON Files (*.json)|*.json";