Moves tree/menu models into the Models.Trees namespace

src/Umbraco.Web/Models/Trees/TreeNodeCollection.cs

@@ -0,0 +1,10 @@
+using System.Collections.Generic;
+using System.Runtime.Serialization;
+
+namespace Umbraco.Web.Models.Trees
+{
+    [CollectionDataContract(Name = "nodes", Namespace = "")]
+    public sealed class TreeNodeCollection : List<TreeNode>
+    {
+    }
+}