优化更新代码，添加界面功能并整合

WPFluent/Controls/TreeModelListView/ITreeModel.cs

@@ -0,0 +1,16 @@
+using System.Collections;
+
+namespace WPFluent.Controls;
+
+public interface ITreeModel
+{
+    /// <summary>
+    /// Get list of children of the specified parent
+    /// </summary>
+    public IEnumerable? GetChildren(object parent);
+
+    /// <summary>
+    /// returns wheather specified parent has any children or not.
+    /// </summary>
+    public bool HasChildren(object parent);
+}