Update copyright headers

Qt copyrights are now in The Qt Company, so we could update the source
code headers accordingly. In the same go we should also fix the links to
point to qt.io.

Change-Id: Ia5781193927251d6b6786f53a9b1cfba9e6d0782
Reviewed-by: Jani Heikkinen <jani.heikkinen@theqtcompany.com>