Added missing license header

src/windows/LocalNotificationProxy/LocalNotificationProxy/LocalNotification/Notification.cs

-namespace LocalNotificationProxy.LocalNotification
+/*
+ * Apache 2.0 License
+ *
+ * Copyright (c) Sebastian Katzer 2017
+ *
+ * This file contains Original Code and/or Modifications of Original Code
+ * as defined in and that are subject to the Apache License
+ * Version 2.0 (the 'License'). You may not use this file except in
+ * compliance with the License. Please obtain a copy of the License at
+ * http://opensource.org/licenses/Apache-2.0/ and read it before using this
+ * file.
+ *
+ * The Original Code and all software distributed under the License are
+ * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
+ * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
+ * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
+ * Please see the License for the specific language governing rights and
+ * limitations under the License.
+ */
+
+namespace LocalNotificationProxy.LocalNotification
 {
     using System;
     using System.Collections.Generic;