Update buck build in Visual Studio

Summary:
- Always launch buck build for Build, but copy native library when it was changed
- Rename Facebook.Yoga.Mac.Test to Facebook.Yoga.Mac.Sample
- Add Facebook.Yoga.Mac.Tests for NUnit test.
  - "Run Unit Tests" menu item was activated for the target, but Mono still can't find libyoga.dylib
Closes https://github.com/facebook/yoga/pull/332

Reviewed By: emilsjolander

Differential Revision: D4408799

Pulled By: splhack

fbshipit-source-id: b3f5f9ebd8265cc152ca859176afbf54efa8f170

csharp/Mac/Facebook.Yoga.Mac.Sample/ViewController.designer.cs

@@ -0,0 +1,18 @@
+// WARNING
+//
+// This file has been generated automatically by Xamarin Studio to store outlets and
+// actions made in the UI designer. If it is removed, they will be lost.
+// Manual changes to this file may not be handled correctly.
+//
+using Foundation;
+
+namespace Facebook.Yoga.Mac.Sample
+{
+	[Register("ViewController")]
+	partial class ViewController
+	{
+		void ReleaseDesignerOutlets()
+		{
+		}
+	}
+}