Update Qt Creator to 3.5.0.

This has been in our experimental area51 repository for a while, and there
is no reason to hold it back.

Release notes:
https://blog.qt.io/blog/2015/08/20/qt-creator-3-5-0-released/
https://blog.qt.io/blog/2015/07/01/qt-creator-3-4-2-released/
https://blog.qt.io/blog/2015/06/02/qt-creator-3-4-1-released/

Thanks to Alonso Schaich (alonso@), Tobias Berner (tcberner@gmail.com) and
Ralf Nolden (nolden@kde.org) for their porting work!