redesign player

[PythonFZ]

Right now, we do render a frame, even if it is no longer displayed. If we do not do this, a frame is only displayed once the slider stops. Ideally, the slider on playback would only go to the next frame once the current one has been rendered.

For the scrubbing this we want to show intermediate frames and have a smooth slider, so there the current implementation might be fine?

Proposal:

• split into displayedFrame and requestFrame