Added task service (#374)

* Added task service

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

@@ -0,0 +1,41 @@
+//
+// 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.TaskServices
+{
+    public class TaskMetadata
+    {
+        /// <summary>
+        /// Task Description
+        /// </summary>
+        public string Description { get; set; }
+
+        /// <summary>
+        /// Task name to define the type of the task e.g. Create Db, back up
+        /// </summary>
+        public string Name { get; set; }
+
+        /// <summary>
+        /// The number of seconds to wait before canceling the task. 
+        /// This is a optional field and 0 or negative numbers means no timeout
+        /// </summary>
+        public int Timeout { get; set; }
+
+        /// <summary>
+        /// Defines if the task can be canceled
+        /// </summary>
+        public bool IsCancelable { get; set; }
+
+        /// <summary>
+        /// Database server name this task is created for
+        /// </summary>
+        public string ServerName { get; set; }
+
+        /// <summary>
+        /// Database name this task is created for
+        /// </summary>
+        public string DatabaseName { get; set; }
+    }
+}