ui: migrate client to gtk

ModpackUpdater.Apps.Client/AppUpdater.cs

@@ -42,7 +42,7 @@ public class AppUpdater
     {
         var client = new HttpClient();
         var tempFileName = Path.GetTempFileName();
-        var appFileName = Pilz.Win32.NativeTools.GetExecutablePath();
+        var appFileName = Environment.ProcessPath;
         var oldFileName = appFileName + ".old";
 
         // Delete old file