pygr: PlotAxes: Stay in log domain if log scale is on.

Modified PlotAxes setWindow method to check domain borders if log
scale is on and stay in that range. All window operations, e.g.
panning, zooming, selection rely on setWindow. Therefore they will
stay in log domain too.
pygr: PlotAxes: Take autoscale into account when staying in log domain

Adjust window accordingly if autoscale and log scale mode are on
in PlotAxes setWindow routine. Ensure that the most recent window will
be used in gr.setwindow by calling PlotAxes' window routine before.
pygr: PlotAxes: Ensure that the most recent window will be used.

Before setting the window using gr.setwindow it has been ensured
that we get the most recent window by calling PlotAxes' window routine.
For calculations afterwards the variables xmin, xmax, ymin, ymax
has not been updated. This has been corrected with this patch.
release v0.5.1