ShowErrorWindow now actually shows the ErrorWindow

PcgsInvUi/Views/ErrorWindow.axaml

@@ -0,0 +1,13 @@
+<Window xmlns="https://github.com/avaloniaui"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+        xmlns:viewModels="clr-namespace:PcgsInvUi.ViewModels"
+        mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
+        x:Class="PcgsInvUi.Views.ErrorWindow" x:DataType="viewModels:ErrorWindowViewModel"
+        Title="ErrorWindow">
+    <Grid RowDefinitions="2">
+        <TextBlock Text="{Binding DisplayedException.Message}" />
+        <Button Content="OK" Command="{Binding CloseCommand}" />
+    </Grid>
+</Window>