Update to use SPDX

[mr-c]

Closes #82

[osallou]

I fully agreee for license, but there should also be a license_file which points to location of the license in the container or at worst to an url
license shoud be no url at all. should be spdx or "self explainatory text such as academic only, see license_file"
and license_file would refer to the url of the license if not available in the container, or its location in the container.