effects/overview: Use out cubic easing curve consistently

The intro and the outro animations are very short and they usually
affect all windows on the screen. Windows have to travel a lot and in
very short time, this doesn't look.

Similar to other windows, this change makes the overview effect use the
out cubic curve for window movements (even though the HIG suggests us
using the InOutCubic easing curve). That way, user will look at
flatter parts of the easing curve more, i.e. the windows would move less
chaotically and simply jump to their target position.

Similar to the WindowHeap, this change makes the overview effect use the
out cubic everywhere else so the intro and the outro animations look
coherent.

Another advantage of the OutCubic easing curve is that it makes the
overview effect look more responsive and subtle.