Create MS.SqlTools.Credentials project (#249)

* Initial credential service files

* Clean-up hostloader

* Update build scripts to build credentials archive

* Move hosting files to new assembly

* Add credentials files to MS.SqlTools.Credentials

* Remove duplicate files

* Update namespace in program.cs

* Fix test build breaks

* Update extensions visibility.

* Remove unused resource strings

* Add xproj files to SLN for appveyor builds

* Fix appveyor build break in test project

* Fix extensibility tests

* Fix various typos in latest iteration

* Add settings for Integration build

* Fix codecoverage.bat to use full pdb for new projects

* Fix bug when packing in folder with native images

* Fix typos in xproj

* Reset XLF to fix build.cmd

src/Microsoft.SqlTools.Hosting/Hosting/Contracts/Shutdown.cs

@@ -0,0 +1,32 @@
+//
+// 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.Hosting.Contracts
+{
+    /// <summary>
+    /// Defines a message that is sent from the client to request
+    /// that the server shut down.
+    /// </summary>
+    public class ShutdownRequest
+    {
+        public static readonly
+            RequestType<object, object> Type =
+            RequestType<object, object>.Create("shutdown");
+    }
+
+    /// <summary>
+    /// Defines an event that is sent from the client to notify that
+    /// the client is exiting and the server should as well.
+    /// </summary>
+    public class ExitNotification
+    {
+        public static readonly
+            EventType<object> Type =
+            EventType<object>.Create("exit");
+    }
+}
+