Change all matplotlib generators to updating

[faymanns]

Generating a new figure for every frame is slow and seems to lead to non deterministic deadlocks.
Updating the data in a single figure and then plotting it with plt.draw() is much faster.
Some generators already use this approach. A good way to implement this might via 'Plotter' classes in utils.py that have a plot method that can be called to generate a frame.