Migrated section controller + LanguageTreeController, ApplciationTreeController.

Updated AngularJsonOnlyConfigurationAttribute to be a TypeFilterAttribute, to allow injeciton into the filter.

Note: Left TODO about checking authorization of proxied trees..

src/Umbraco.Web.BackOffice/Trees/LanguageTreeController.cs

@@ -0,0 +1,56 @@
+using Microsoft.AspNetCore.Http;
+using Umbraco.Core.Services;
+using Umbraco.Web.BackOffice.Filters;
+using Umbraco.Web.BackOffice.Trees;
+using Umbraco.Web.Common.Attributes;
+using Umbraco.Web.Models.Trees;
+using Umbraco.Web.WebApi;
+using Constants = Umbraco.Core.Constants;
+
+namespace Umbraco.Web.Trees
+{
+    [UmbracoTreeAuthorize(Constants.Trees.Languages)]
+    [Tree(Constants.Applications.Settings, Constants.Trees.Languages, SortOrder = 11, TreeGroup = Constants.Trees.Groups.Settings)]
+    [PluginController("UmbracoTrees")]
+    [CoreTree]
+    public class LanguageTreeController : TreeController
+    {
+
+        public LanguageTreeController(
+            ILocalizedTextService textService,
+            UmbracoApiControllerTypeCollection umbracoApiControllerTypeCollection)
+            : base(textService, umbracoApiControllerTypeCollection)
+        {
+        }
+        protected override TreeNodeCollection GetTreeNodes(string id, FormCollection queryStrings)
+        {
+            //We don't have any child nodes & only use the root node to load a custom UI
+            return new TreeNodeCollection();
+        }
+
+        protected override MenuItemCollection GetMenuForNode(string id, FormCollection queryStrings)
+        {
+            //We don't have any menu item options (such as create/delete/reload) & only use the root node to load a custom UI
+            return null;
+        }
+
+        /// <summary>
+        /// Helper method to create a root model for a tree
+        /// </summary>
+        /// <returns></returns>
+        protected override TreeNode CreateRootNode(FormCollection queryStrings)
+        {
+            var root = base.CreateRootNode(queryStrings);
+
+            //this will load in a custom UI instead of the dashboard for the root node
+            root.RoutePath = $"{Constants.Applications.Settings}/{Constants.Trees.Languages}/overview";
+            root.Icon = "icon-globe";
+            root.HasChildren = false;
+            root.MenuUrl = null;
+
+            return root;
+        }
+
+
+    }
+}