Feature/connect cancel (#74)

* Implemented connection cancellation

* Made connect requests return immediately and created a separate connection complete notification

* Fix spelling

* Fix sorting

* Add separate lock for cancellation source map

src/Microsoft.SqlTools.ServiceLayer/Connection/Contracts/CancelConnectRequest.cs

@@ -0,0 +1,19 @@
+//
+// 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.ServiceLayer.Hosting.Protocol.Contracts;
+
+namespace Microsoft.SqlTools.ServiceLayer.Connection.Contracts
+{
+    /// <summary>
+    /// Cancel connect request mapping entry 
+    /// </summary>
+    public class CancelConnectRequest
+    {
+        public static readonly
+            RequestType<CancelConnectParams, bool> Type =
+            RequestType<CancelConnectParams, bool>.Create("connection/cancelconnect");
+    }
+}