add toolbar-free mouse panning and zooming to the plot

Connect matplotlib event handlers on the plot canvas so the display
can be navigated without engaging the toolbar modes: left button
drag pans the view, the mouse wheel zooms both axes around the
pointer, and right button drag zooms single axes (horizontal motion
zooms x, vertical motion zooms y, like the right button in the
toolbar pan mode). Linear (including inverted ppm) and logarithmic
axes are handled, the latter in log space. While a toolbar pan/zoom
mode is active the handlers stand back so the toolbar behavior is
unchanged. Documented in doc/manual.rst.

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

doc/manual.rst

@@ -100,6 +100,8 @@ There are now two possibilities to export the figure:
 1. Saving the plot as a figure (EPS, PNG, JPEG and more) by pressing the save button in the toolbar below the plot area
 2. Saving the data of the plot as CSV file (comma separated values) by pressing the button on the right side of the toolbar under the plot
 
+The plot can be navigated directly with the mouse: dragging with the left mouse button pans the view and the mouse wheel zooms in and out around the pointer position. Holding the right mouse button and dragging horizontally zooms only the x axis, dragging vertically zooms only the y axis (dragging right or up zooms in), just like the right button in the toolbar pan mode. This works on linear and logarithmic axes. The pan and zoom buttons in the toolbar below the plot are still available; while one of these toolbar modes is active, the direct mouse panning and right-button zooming are suspended so the toolbar behavior is unchanged. Note that with the autoscaling option enabled, the view is reset to the full data range whenever a new result arrives.
+
 
 Help Menu
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