add Watermark

src/Shared/HandyControl_Shared/Themes/Styles/Watermark.xaml

@@ -0,0 +1,10 @@
+<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+                    xmlns:controls="clr-namespace:HandyControl.Controls">
+    
+    <ResourceDictionary.MergedDictionaries>
+        <ResourceDictionary Source="Base/WatermarkBaseStyle.xaml"/>
+    </ResourceDictionary.MergedDictionaries>
+
+    <Style BasedOn="{StaticResource WatermarkBaseStyle}" TargetType="controls:Watermark"/>
+
+</ResourceDictionary>