Object Explorer Service (#311)

* moving OE service from an old branch

src/Microsoft.SqlTools.ServiceLayer/ObjectExplorer/Contracts/NodeInfo.cs

@@ -0,0 +1,40 @@
+//
+// 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.ObjectExplorer.Contracts
+{
+    /// <summary>
+    /// Information describing a Node in the Object Explorer tree. 
+    /// Contains information required to display the Node to the user and
+    /// to know whether actions such as expanding children is possible
+    /// the node 
+    /// </summary>
+    public class NodeInfo
+    {
+        /// <summary>
+        /// Path identifying this node: for example a table will be at ["server", "database", "tables", "tableName"].
+        /// This enables rapid navigation of the tree without the need for a global registry of elements.
+        /// The path functions as a unique ID and is used to disambiguate the node when sending requests for expansion.
+        /// A common ID is needed since processes do not share address space and need a unique identifier
+        /// </summary>
+        public string NodePath { get; set; }
+
+        /// <summary>
+        /// The type of the node - for example Server, Database, Folder, Table
+        /// </summary>
+        public string NodeType { get; set; }
+
+        /// <summary>
+        /// Label to display to the user, describing this node.
+        /// </summary>
+        public string Label { get; set; }
+
+        /// <summary>
+        /// Is this a leaf node (in which case no children can be generated) or
+        /// is it expandable?
+        /// </summary>
+        public bool IsLeaf { get; set; }
+    }
+}