Update LICENSE.txt and license header on files.

LICENSE.txt

@@ -1,4 +1,4 @@
-Copyright (c) Microsoft Open Technologies, Inc. All rights reserved.
+Copyright (c) .NET Foundation. All rights reserved.
 
 Licensed under the Apache License, Version 2.0 (the "License"); you may not use
 these files except in compliance with the License. You may obtain a copy of the