update or add copyright and license info to source files

[juagargi]

Similar as in scionproto, place at the beginning of the file:

// Copyright 2019 ETH Zurich
//
// 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.package main

[matzf]

Looks like this is applied consistently now (c38e2d0). Now I see the source of this mysterious package main at the end of the text 😄