App: Fix errors on startup

Elwig/App.xaml

@@ -3,7 +3,6 @@
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:ctrl="clr-namespace:Elwig.Controls"
-        StartupUri="Windows\MainWindow.xaml"
         Exit="Application_Exit">
     <Application.Resources>
         <ctrl:BoolToStringConverter x:Key="BoolToStarConverter" FalseValue="" TrueValue="*"/>

Elwig/App.xaml.cs

@@ -17,6 +17,7 @@ using Elwig.Dialogs;
 using System.Threading.Tasks;
 using Elwig.Helpers.Billing;
 using Elwig.Models.Entities;
+using System.Text;
 
 namespace Elwig {
     public partial class App : Application {
@@ -65,7 +66,7 @@ namespace Elwig {
         private readonly DispatcherTimer ContextTimer = new() { Interval = TimeSpan.FromSeconds(2) };
 
         public App() : base() {
-            System.Text.Encoding.RegisterProvider(System.Text.CodePagesEncodingProvider.Instance);
+            Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);
             Directory.CreateDirectory(TempPath);
             Directory.CreateDirectory(DataPath);
             MainDispatcher = Dispatcher;
@@ -178,6 +179,9 @@ namespace Elwig {
             }
 
             base.OnStartup(evt);
+
+            var window = new MainWindow();
+            window.Show();
         }
 
         private async void Application_Exit(object sender, ExitEventArgs evt) {