Initial admin and DR services. (#329)

* Add initial services for admin, tasks, and DR

* Fix up some of the contract interfaces

* Make fields public to allow Json.Net to work

* Fix a couple issues in backup contracts

src/Microsoft.SqlTools.ServiceLayer/TaskServices/TaskService.cs

@@ -0,0 +1,52 @@
+//
+// 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;
+using Microsoft.SqlTools.ServiceLayer.Hosting;
+using Microsoft.SqlTools.ServiceLayer.SqlContext;
+using Microsoft.SqlTools.ServiceLayer.TaskServices.Contracts;
+using System;
+using System.Threading.Tasks;
+
+namespace Microsoft.SqlTools.ServiceLayer.TaskServices
+{
+    public class TaskService
+    {
+        private static readonly Lazy<TaskService> instance = new Lazy<TaskService>(() => new TaskService());
+
+        /// <summary>
+        /// Default, parameterless constructor.
+        /// </summary>
+        internal TaskService()
+        {
+        }
+
+        /// <summary>
+        /// Gets the singleton instance object
+        /// </summary>
+        public static TaskService Instance
+        {
+            get { return instance.Value; }
+        }
+
+        /// <summary>
+        /// Initializes the service instance
+        /// </summary>
+        public void InitializeService(ServiceHost serviceHost, SqlToolsContext context)
+        {
+            serviceHost.SetRequestHandler(ListTasksRequest.Type, HandleListTasksRequest);
+        }
+
+        /// <summary>
+        /// Handles a list tasks request
+        /// </summary>
+        internal static async Task HandleListTasksRequest(
+            ListTasksParams listTasksParams,
+            RequestContext<ListTasksResponse> requestContext)
+        {
+            await requestContext.SendResult(new ListTasksResponse());
+        }
+    }
+}