Add live_view module to qutil.plotting.

The live_view module provides a matplotlib interface for concurrent data viewing using animations and blitting. For line plots without axis rescaling, frame rates of ~100 fps can be reached. A 1080x1920 pixel image can be displayed at ~20 fps. Data sources are pushed to a background thread from where they can fill a queue.

See mjolnir commits a771a5cc..205318e6 for earlier history.

qutil/plotting/live_view.py

@@ -1073,6 +1073,8 @@ class BatchedLiveView1D(LiveView1DBase):
     >>> view.start()
     >>> plt.pause(0.1)  # Only here for doctest
 
+    >>> view.stop()
+
     If the data update rate is slow, blitting together with automatic
     rescaling might lead to a white canvas being visible between a
     rescale being triggered and new data being drawn. In this case you