License maintenance: GPLv2 -> GPLv2+
Summary:
This should now cover all remaining GPLv2-only files in pimcommon,
excluding test code. This is based on existing approval from
https://techbase.kde.org/Projects/KDE_Relicensing.
Reviewers: mlaurent
Reviewed By: mlaurent
Subscribers: kde-pim
Tags: KDE PIM
Differential Revision: https://phabricator.kde.org/D16477