Object Explorer Service (#311)

* moving OE service from an old branch

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

@@ -0,0 +1,45 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using Microsoft.SqlTools.Hosting.Protocol.Contracts;
+using Microsoft.SqlTools.ServiceLayer.Connection.Contracts;
+
+namespace Microsoft.SqlTools.ServiceLayer.ObjectExplorer.Contracts
+{
+    /// <summary>
+    /// Information returned from a <see cref="CreateSessionRequest"/>.
+    /// Contains success information, a <see cref="SessionId"/> to be used when
+    /// requesting expansion of nodes, and a root node to display for this area.
+    /// </summary>
+    public class CreateSessionResponse
+    {
+        /// <summary>
+        /// Boolean indicating if the connection was successful
+        /// </summary>
+        public bool Success { get; set; }
+
+        /// <summary>
+        /// Unique ID to use when sending any requests for objects in the
+        /// tree under the node
+        /// </summary>
+        public string SessionId { get; set; }
+
+        /// <summary>
+        /// Information describing the base node in the tree
+        /// </summary>
+        public NodeInfo RootNode { get; set; }
+    }
+    /// <summary>
+    /// Establishes an Object Explorer tree session for a specific connection.
+    /// This will create a connection to a specific server or database, register
+    /// it for use in the 
+    /// </summary>
+    public class CreateSessionRequest
+    {
+        public static readonly
+            RequestType<ConnectionDetails, CreateSessionResponse> Type =
+            RequestType<ConnectionDetails, CreateSessionResponse>.Create("objectexplorer/createsession");
+    }
+}