WinGui: Make the Dark Theme Windows 10 only.

win/CS/HandBrakeWPF/App.xaml.cs

@@ -122,7 +122,7 @@ namespace HandBrakeWPF
             }
 
             bool useDarkTheme = userSettingService.GetUserSetting<bool>(UserSettingConstants.UseDarkTheme);
-            if (useDarkTheme)
+            if (useDarkTheme && SystemInfo.IsWindows10())
             {
                 ResourceDictionary darkTheme = new ResourceDictionary();
                 darkTheme.Source = new Uri("Themes/Dark.xaml", UriKind.Relative);

win/CS/HandBrakeWPF/Properties/Resources.Designer.cs

@@ -2633,7 +2633,7 @@ namespace HandBrakeWPF.Properties {
         }
         
         /// <summary>
-        ///   Looks up a localized string similar to Use the Dark Theme. (Requires Restart)  (THIS IS AN EARLY PREVIEW. IT IS NOT YET COMPLETE!).
+        ///   Looks up a localized string similar to Use the Dark Theme. (Requires Restart, Windows 10 only).
         /// </summary>
         public static string Options_DarkTheme {
             get {

win/CS/HandBrakeWPF/Properties/Resources.resx

@@ -1992,7 +1992,7 @@ Where supported, any user presets will have been imported.</value>
     <value>Export Queue (CLI Only)</value>
   </data>
   <data name="Options_DarkTheme" xml:space="preserve">
-    <value>Use the Dark Theme. (Requires Restart)  (THIS IS AN EARLY PREVIEW. IT IS NOT YET COMPLETE!)</value>
+    <value>Use the Dark Theme. (Requires Restart, Windows 10 only)</value>
   </data>
   <data name="QueueView_NotAvailable" xml:space="preserve">
     <value>Not Available</value>

win/CS/HandBrakeWPF/ViewModels/OptionsViewModel.cs

@@ -190,6 +190,8 @@ namespace HandBrakeWPF.ViewModels
             }
         }
 
+        public bool IsWindows10 => HandBrakeWPF.Utilities.SystemInfo.IsWindows10();
+
         #region General
 
         public BindingList<InterfaceLanguage> InterfaceLanguages

win/CS/HandBrakeWPF/Views/OptionsView.xaml

@@ -116,7 +116,7 @@
                         </StackPanel>
 
                         <StackPanel Orientation="Vertical" Margin="20,5,0,0">
-                            <CheckBox Content="{x:Static Properties:Resources.Options_DarkTheme}" IsChecked="{Binding UseDarkTheme}" />
+                            <CheckBox Content="{x:Static Properties:Resources.Options_DarkTheme}" IsEnabled="{Binding IsWindows10}" IsChecked="{Binding UseDarkTheme}" />
                             <CheckBox Content="{x:Static Properties:Resources.Options_MinimiseTray}" IsChecked="{Binding MinimiseToTray}" />
                             <CheckBox Content="{x:Static Properties:Resources.Options_ClearCompleted}" IsChecked="{Binding ClearQueueOnEncodeCompleted}" />
                             <CheckBox Content="{x:Static Properties:Resources.OptionsView_ShowStatusInTitleBar}" IsChecked="{Binding ShowStatusInTitleBar}" />