ShowErrorWindow now actually shows the ErrorWindow

PcgsInvUi/ViewModels/ErrorWindowViewModel.cs

@@ -0,0 +1,22 @@
+using System;
+using System.Reactive;
+using ReactiveUI;
+using PcgsInvUi.Views;
+
+namespace PcgsInvUi.ViewModels; 
+
+public class ErrorWindowViewModel : ViewModelBase {
+
+    public Exception DisplayedException {
+        get => _message;
+        set => this.RaiseAndSetIfChanged(ref _message, value);
+    }
+
+    private Exception _message;
+
+    public ReactiveCommand<ErrorWindow, Unit> CloseCommand { get; }
+    
+    public ErrorWindowViewModel(string message) {
+        CloseCommand = ReactiveCommand.Create<ErrorWindow>(window => { window.Close(); });
+    }
+}