Add license header to python files in add-on check

[MartijnKaijser]

It's encouraged that every python (or whatever) file has a short license reference at the top.

Copyright (C) 2018-2018 Team Kodi
This file is part of Kodi - https://kodi.tv

SPDX-License-Identifier: GPL-3.0-only
See LICENSES/README.md for more information.

[mzfr]

@MartijnKaijser This one is connected to #126
So now we want to first check if the license exists or not and if it doesn't then we just add it?

[MartijnKaijser]

It's not connected. Add-on check itself also needs a license header in the Py files

[mzfr]

oh, you mean like files in this tool. I thought we have to add it when we are checking the addons. Sorry, my bad :)