Updated license headers

From Qt 5.7 -> LGPL v2.1 isn't an option anymore, see
http://blog.qt.io/blog/2016/01/13/new-agreement-with-the-kde-free-qt-foundation/


Updated license headers to use new LGPL header instead of LGPL21 one
(in those files which will be under LGPL v3)

Change-Id: I25237f97989d42da1130ed5c0839c31eb3904d34
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
Reviewed-by: Jani Heikkinen <jani.heikkinen@qt.io>