Draft: Change audio position update interval to 30Hz

This MR makes GStreamer report the audio position 30 times per second, which seems to be a nice sweet spot between smoothness and performance.

I currently recommend NOT merging this with the Cairo waveform implementation. The current waveform leaks memory every frame, has mathematical issues making the waveform move back and forth, and is too inefficient justify the added visual clarity.

I have another waveform rewrite not published yet which fixes all these issues while reducing the CPU usage to less than !76 uses at 10 fps.