Convert license statements to SPDX
Summary:
Convert license statements to SPDX and add required files in LICENSES
folder.
Reviewers: cgiboudeaux
Reviewed By: cgiboudeaux
Subscribers: cgiboudeaux, kde-frameworks-devel
Tags: Frameworks
Maniphest Tasks: T11550
Differential Revision: https://phabricator.kde.org/D27091