KHolidays: Convert license statements to SPDX expressions
Summary:
Convert license statements to SPDX markers and
add license files as required by REUSE specification.
Reviewers: winterz
Reviewed By: winterz
Subscribers: cgiboudeaux, winterz, kde-frameworks-devel
Tags: Frameworks
Maniphest Tasks: T11550
Differential Revision: https://phabricator.kde.org/D27363