support for .NET framework 3.5

Still have bugs

Net35/HandyControlDemo_Net35/Data/Model/StepBarDemoModel.cs

@@ -0,0 +1,9 @@
+namespace HandyControlDemo.Data
+{
+    public class StepBarDemoModel
+    {
+        public string Header { get; set; }
+
+        public string Content { get; set; }
+    }
+}