Fix namespaces for code moved to separate class libraries (#263)

* Create ServiceHost a service-specific class

* Renaming hosting namespace

* Rename credentials namespace

* Fix namespaces

src/Microsoft.SqlTools.Hosting/Utility/AsyncContextThread.cs

@@ -7,7 +7,7 @@ using System;
 using System.Threading;
 using System.Threading.Tasks;
 
-namespace Microsoft.SqlTools.ServiceLayer.Utility
+namespace Microsoft.SqlTools.Utility
 {
     /// <summary>
     /// Provides a simplified interface for creating a new thread