Change license for network remote protocol buffer meassages to Apache

ext/libclementine-remote/remotecontrolmessages.proto

@@ -1,3 +1,23 @@
+/* This file is part of Clementine.
+   Copyright 2017, David Sansome <me@davidsansome.com>
+   Copyright 2017, Andreas Muttscheller <asfa194@gmail.com>
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+// Note: this file is licensed under the Apache License instead of GPL, so 
+// 3rd party applications or libraries can use another license besides GPL.
+
 package pb.remote;
 
 // The supported message types