support for .NET framework 3.5

Still have bugs

Net35/HandyControlDemo_Net35/Resources/Themes/Basic/Converters.xaml

@@ -0,0 +1,7 @@
+<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    xmlns:converter="clr-namespace:HandyControlDemo.Tools.Converter">
+
+    <converter:StringRepeatConverter x:Key="StringRepeatConverter"/>
+
+</ResourceDictionary>