UI - Fix possible exception when showing dialogs

Profile editor - Limit undo/redo to 20 actions for now
Plugins - Fix custom icons not displaying in settings windows

src/Artemis.UI/Screens/Settings/Tabs/Plugins/PluginSettingsWindowView.xaml

@@ -26,7 +26,14 @@
         <DockPanel>
             <controls:AppBar Type="Dense" Title="{Binding  ActiveItem.Plugin.Info.Name}" DockPanel.Dock="Top" Margin="-18 0 0 0" ShowShadow="False">
                 <controls:AppBar.AppIcon>
-                    <shared:ArtemisIcon Icon="{Binding Icon}"></shared:ArtemisIcon>
+                    <shared:ArtemisIcon Icon="{Binding Plugin.Info.ResolvedIcon}"
+                                        Margin="0 5 0 0"
+                                        Width="20"
+                                        Height="20"
+                                        Grid.Row="0"
+                                        Grid.RowSpan="3"
+                                        HorizontalAlignment="Center"
+                                        VerticalAlignment="Top" />
                 </controls:AppBar.AppIcon>
             </controls:AppBar>
 

src/Artemis.UI/Screens/Settings/Tabs/Plugins/PluginSettingsWindowViewModel.cs

@@ -1,4 +1,5 @@
 using System;
+using Artemis.Core;
 using Artemis.UI.Shared;
 using Stylet;
 
@@ -11,10 +12,10 @@ namespace Artemis.UI.Screens.Settings.Tabs.Plugins
         public PluginSettingsWindowViewModel(PluginConfigurationViewModel configurationViewModel)
         {
             _configurationViewModel = configurationViewModel ?? throw new ArgumentNullException(nameof(configurationViewModel));
-            Icon = configurationViewModel.Plugin.Info.Icon;
+            Plugin = configurationViewModel.Plugin;
         }
 
-        public object Icon { get; }
+        public Plugin Plugin { get; }
 
         protected override void OnInitialActivate()
         {