Provide EVENT_XAXIS_SCALE and EVENT_YAXIS_SCALE events

[Wolfgang]

Hello,

I miss an event that is fired whenever an axis, set to autoscale, changes its minimum/maximum values.

Imagine the following scenario: On a xy graph, I have several plots and also some 'regions of interest' that are visualized either by lines or rectangles. Now, if a new plot is added that results in a different axis scale, I also need to redraw my regions of interest. At present, this requires bookkeeping of xmin, xmax, ymin, ymax and comparing the current axes ranges with the previous ones. It appears to be simpler if one could rely on a suitable event that is fired whenever the axis range is changed.

Thanks