pygr: Add setWCforPlotAxes method.

Define world coordinates (WC) for a coordinate system (PlotAxes) to allow
translation from axes coordinates which corresponds to world coordinates to
device- (DC) and/or normalized device coordinates (NDC).

Change-Id: Ia8dd47551a5fa68af236c342f557f9b1ef13a777
Reviewed-on: https://iffwww.iff.kfa-juelich.de/review/52
Reviewed-by: Josef Heinen <j.heinen@fz-juelich.de>
Preserve matplotlib 1.3 backward compatibility

Change-Id: Ic0ed720ed093cf66e1a359497a466cec2276b65a
Reviewed-on: https://iffwww.iff.kfa-juelich.de/review/53
Reviewed-by: Josef Heinen <j.heinen@fz-juelich.de>
Allow line breaks in text output (gr_text)

Change-Id: Id65539870751698b73b760a97c48ad049b640500
Reviewed-on: https://iffwww.iff.kfa-juelich.de/review/57
Reviewed-by: Josef Heinen <j.heinen@fz-juelich.de>