support for .NET framework 3.5

Still have bugs

Net35/HandyControl_Net35/Interactivity/TriggerAction!1.cs

@@ -0,0 +1,19 @@
+using System;
+using System.Windows;
+
+namespace HandyControl.Interactivity
+{
+    public abstract class TriggerAction<T> : TriggerAction where T : DependencyObject
+    {
+        protected TriggerAction() : base(typeof(T))
+        {
+        }
+
+#pragma warning disable 108,114
+        protected T AssociatedObject => (T)base.AssociatedObject;
+#pragma warning restore 108,114
+
+        protected sealed override Type AssociatedObjectTypeConstraint =>
+            base.AssociatedObjectTypeConstraint;
+    }
+}