Create remote file browser service (#448)

* code refactoring

* Add filebrowser service and tests

* change dataset reference

* Address pr comments

* add more tests

* address pr comments

* address pr comments and added more tests

* minor change

* minor fix

* Fix test break and add dataset result check

src/Microsoft.SqlTools.ServiceLayer/FileBrowser/Contracts/FileTree.cs

@@ -0,0 +1,31 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+namespace Microsoft.SqlTools.ServiceLayer.FileBrowser.Contracts
+{
+    /// <summary>
+    /// Tree to represent file/folder structure
+    /// </summary>
+    public class FileTree
+    {
+        /// <summary>
+        /// Root node of the tree
+        /// </summary>
+        public FileTreeNode RootNode { get; private set; }
+
+        /// <summary>
+        /// Selected node of the tree
+        /// </summary>
+        public FileTreeNode SelectedNode { get; set; }
+
+        /// <summary>
+        /// Constructor
+        /// </summary>
+        public FileTree()
+        {
+            this.RootNode = new FileTreeNode();
+        }
+    }
+}