improve disabled states on radios and checks. fixes #500

Author: ButchersBoy

MainDemo.Wpf/Buttons.xaml

@@ -247,7 +247,7 @@
                     Mate
                 </CheckBox>
                 <CheckBox Style="{StaticResource MaterialDesignCheckBox}" Margin="0 0 8 8" VerticalAlignment="Center" 
-                      IsEnabled="False">
+                          IsEnabled="False"  IsChecked="True">
                     Disabled
                 </CheckBox>
             </StackPanel>

MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.CheckBox.xaml

@@ -114,7 +114,7 @@
                         </Trigger>
                         <Trigger Property="IsEnabled" Value="False">
                             <Setter Property="Fill" TargetName="Graphic" Value="{DynamicResource MaterialDesignCheckBoxDisabled}" />
-                            <Setter TargetName="contentPresenter" Property="Opacity" Value="0.79"/>
+                            <Setter Property="Opacity" Value="0.26"/>
                         </Trigger>
                         <Trigger Property="IsPressed" Value="true"/>
                         <Trigger Property="IsChecked" Value="true">
@@ -213,7 +213,7 @@
                             <Setter Property="Padding" Value="4,2,0,0"/>
                         </Trigger>
                         <Trigger Property="IsEnabled" Value="false">
-                            <Setter Property="Opacity" TargetName="Graphic" Value=".56" />
+                            <Setter Property="Opacity" TargetName="Graphic" Value=".26" />
                         </Trigger>
                         <Trigger Property="IsPressed" Value="true"/>
                         <Trigger Property="IsChecked" Value="true">

MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.RadioButton.xaml

@@ -85,7 +85,7 @@
                         </Trigger>
                         <Trigger Property="IsEnabled" Value="false">
                             <Setter Property="Fill" TargetName="Graphic" Value="{DynamicResource MaterialDesignCheckBoxDisabled}" />
-                            <Setter TargetName="contentPresenter" Property="Opacity" Value="0.79"/>
+                            <Setter Property="Opacity" Value="0.26"/>
                         </Trigger>
                         <Trigger Property="IsPressed" Value="true"/>
                         <Trigger Property="IsChecked" Value="true">