Relicense some files to LGPL2.1+

This has been done with approval from the original authors (including
myself).

Some are still GPL-2.0. I will contact the author(s) to handle that.

CCMAIL: mart@kde.org
CCMAIL: hein@kde.org
CCMAIL: kde@privat.broulik.de
CCMAIL: kde-frameworks-devel@kde.org