Added ticks on ImageBlendSlider, at 0%, 50% and 100%

Author: goran-w

src/Views/ImageDiffView.axaml

@@ -140,7 +140,8 @@
                   x:Name="ImageBlendSlider"
                   Minimum="0" Maximum="1"
                   VerticalAlignment="Top"
-                  TickPlacement="None"
+                  TickFrequency="0.5"
+                  TickPlacement="BottomRight"
                   Margin="0"
                   MinHeight="0"
                   Foreground="{DynamicResource Brush.Border1}"