Show unhandled exceptions to users

DiscordChatExporter.Gui/App.xaml

@@ -4,6 +4,7 @@
     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
     xmlns:converters="clr-namespace:DiscordChatExporter.Gui.Converters"
     xmlns:local="clr-namespace:DiscordChatExporter.Gui"
+    DispatcherUnhandledException="App_OnDispatcherUnhandledException"
     StartupUri="Views/MainWindow.xaml">
     <Application.Resources>
         <ResourceDictionary>

DiscordChatExporter.Gui/App.xaml.cs

@@ -1,6 +1,13 @@
-namespace DiscordChatExporter.Gui
+using System.Windows;
+using System.Windows.Threading;
+
+namespace DiscordChatExporter.Gui
 {
     public partial class App
     {
+        private void App_OnDispatcherUnhandledException(object sender, DispatcherUnhandledExceptionEventArgs args)
+        {
+            MessageBox.Show(args.Exception.ToString(), "Error occured", MessageBoxButton.OK, MessageBoxImage.Error);
+        }
     }
 }