Fix license text and URLs in QMessageBox::aboutQt().

Point to new qt.io site, adapt licensing text.

Task-number: QTBUG-41798
Change-Id: I492df6a842c2b31e44653fb4388408c209f24f1e
Reviewed-by: Sami Makkonen <sami.makkonen@digia.com>
Reviewed-by: Jani Heikkinen <jani.heikkinen@digia.com>
(cherry picked from qtbase/4a2cf9ca4174ee9879bfc5858f10dacc028a521f)
Reviewed-by: Lars Knoll <lars.knoll@digia.com>