support for .NET framework 3.5

Still have bugs

Net35/HandyControl_Net35/Themes/Styles/GroupBox.xaml

@@ -0,0 +1,14 @@
+<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+
+    <ResourceDictionary.MergedDictionaries>
+        <ResourceDictionary Source="Base/GroupBoxBaseStyle.xaml"/>
+    </ResourceDictionary.MergedDictionaries>
+
+    <Style BasedOn="{StaticResource GroupBoxBaseStyle}" TargetType="GroupBox"/>
+
+    <Style x:Key="GroupBoxOriginal" BasedOn="{StaticResource GroupBoxOriginalBaseStyle}" TargetType="GroupBox"/>
+
+    <Style x:Key="GroupBoxTab" BasedOn="{StaticResource GroupBoxTabBaseStyle}" TargetType="GroupBox"/>
+
+</ResourceDictionary>