Added ExpandAll(), CollapseAll() and Collapsed() functions to GridTreeuiComponent

inabox.wpf/DynamicGrid/UIComponent/DynamicGridTreeUIComponent.cs

@@ -163,6 +163,11 @@ public class DynamicGridTreeUIComponent<T, TKey> : IDynamicGridUIComponent<T>, I
         }
     }
 
+    public void ExpandAll() => _tree.ExpandAllNodes();
+    public void CollapseAll() => _tree.CollapseAllNodes();
+
+    public bool Collapsed() => _tree.View.Nodes.Any(x => x.IsExpanded) == false;
+
     private double minRowHeight = 30D;
     private double maxRowHeight = 30D;