The KWin::TimeLine class was only a small wrapper around QTimeLine
without adding anything to QTimeLine what is not present in QTimeLine.
The initial idea was to make it possible to provide more curve shapes.
This is now obsoleted by Qt shipping more useful curves with QTimeLine.
So let's clean up a little bit and use QTimeLine directly instead of
the small wrapper.
All effects are adjusted to use QTimeLine directly.