Ki18n: Convert license headers to SPDX statements
Summary:
Convert license statements to SPDX and add license text files in LICENSES
folder as required by the REUSE specification.
Reviewers: cgiboudeaux
Reviewed By: cgiboudeaux
Subscribers: kossebau, cgiboudeaux, kde-frameworks-devel
Tags: Frameworks
Maniphest Tasks: T11550
Differential Revision: https://phabricator.kde.org/D27245