pygr: Scale PlotAxes window in respect to ErrorBars.

If an error bar's center is inside the current window adjust
margins to contain error bars.

Change-Id: Id4641c8fe2472da0e8887ded9cbeac755ddc656a
Reviewed-on: https://iffwww.iff.kfa-juelich.de/review/72
Reviewed-by: Christian Felder <c.felder@fz-juelich.de>
Reviewed-by: Josef Heinen <j.heinen@fz-juelich.de>