More license maintenance: GPLv2 -> GPLv2+
Summary:
This should now cover all remaining GPLv2-only files in messagelib,
excluding test code. This is largely based on existing approval from
https://techbase.kde.org/Projects/KDE_Relicensing.
Missing are KDAB (hereby approved) and Andras (hopefully approving by
+2'ing this review).
Reviewers: amantia
Reviewed By: amantia
Subscribers: kde-pim
Tags: KDE PIM
Differential Revision: https://phabricator.kde.org/D16000