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/Contracts/ListTasksRequest.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.
+//
+
+using Microsoft.SqlTools.Hosting.Protocol.Contracts;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+
+namespace Microsoft.SqlTools.ServiceLayer.TaskServices.Contracts
+{
+
+    public class ListTasksParams
+    {
+        bool ListActiveTasksOnly { get; set; }        
+    }
+
+    public class ListTasksResponse
+    {
+        TaskInfo[] Tasks { get; set; }
+    }
+
+    public class ListTasksRequest
+    {
+        public static readonly
+            RequestType<ListTasksParams, ListTasksResponse> Type =
+                RequestType<ListTasksParams, ListTasksResponse>.Create("tasks/listtasks");
+    }
+}

src/Microsoft.SqlTools.ServiceLayer/TaskServices/Contracts/TaskInfo.cs

@@ -0,0 +1,21 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+
+namespace Microsoft.SqlTools.ServiceLayer.TaskServices.Contracts
+{
+    public enum TaskState
+    {
+        NotStarted = 0,
+        Running = 1,
+        Complete = 2
+    }
+
+    public class TaskInfo
+    {
+        public int TaskId { get; set;  }
+
+        public TaskState State { get;  set; }
+    }
+}

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());
+        }
+    }
+}