Add v2 of the Hosting Service and build nuget packages for it (#675)

* Port v2 of Hosting service to SqlToolsService
- Renamed project to .v2 so that existing hosted service isn't impacted
- Copied over the CoreServices project which contains ConnectionServiceCore and other reusable services for anything interacting with MSSQL
- Ported unit test project across and verified tests run.

* Nuget package support for reusable DLLs

* Use 1.1 version per Karl's suggestion

* Use correct license URL and project URL

* Use new SMO packages

src/Microsoft.SqlTools.Hosting.v2/Protocol/MessageWriter.cs

@@ -0,0 +1,59 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using System.IO;
+using System.Text;
+using System.Threading.Tasks;
+using Microsoft.SqlTools.Hosting.Utility;
+
+namespace Microsoft.SqlTools.Hosting.Protocol
+{
+    public class MessageWriter
+    {
+        private const string ContentLength = "Content-Length: ";
+        private const string ContentType = "Content-Type: application/json";
+        private const string HeaderSeparator = "\r\n";
+        private const string HeaderEnd = "\r\n\r\n";
+
+        private readonly Stream outputStream;
+        private readonly AsyncLock writeLock = new AsyncLock();
+
+        public MessageWriter(Stream outputStream)
+        {
+            Validate.IsNotNull("streamWriter", outputStream);
+
+            this.outputStream = outputStream;
+        }
+        
+        public virtual async Task WriteMessage(Message messageToWrite)
+        {
+            Validate.IsNotNull("messageToWrite", messageToWrite);
+
+            // Log the JSON representation of the message
+            string logMessage = string.Format("Sending message of type[{0}] and method[{1}]",
+                messageToWrite.MessageType, messageToWrite.Method);
+            Logger.Instance.Write(LogLevel.Verbose, logMessage);
+
+            string serializedMessage = messageToWrite.Serialize();
+            // TODO: Allow encoding to be passed in
+            byte[] messageBytes = Encoding.UTF8.GetBytes(serializedMessage);
+
+            string headers = ContentLength + messageBytes.Length + HeaderSeparator
+                             + ContentType + HeaderEnd;
+            byte[] headerBytes = Encoding.ASCII.GetBytes(headers);
+
+            // Make sure only one call is writing at a time.  You might be thinking
+            // "Why not use a normal lock?"  We use an AsyncLock here so that the
+            // message loop doesn't get blocked while waiting for I/O to complete.
+            using (await writeLock.LockAsync())
+            {
+                // Send the message
+                await outputStream.WriteAsync(headerBytes, 0, headerBytes.Length);
+                await outputStream.WriteAsync(messageBytes, 0, messageBytes.Length);
+                await outputStream.FlushAsync();
+            }
+        }
+    }
+}