Add Copyright headers where missing in handlers

- Added Copyright in handlers where missing
- Renamed Project to Author(s) where needed

Signed-off-by: Alex Ellis (VMware) <alexellis2@gmail.com>

gateway/handlers/forwarding_proxy_test.go

@@ -1,3 +1,6 @@
+// Copyright (c) OpenFaaS Author(s). All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
 package handlers
 
 import (