hardware accelerated surface plots in gr3.

new 'accelerate' flag in pygr.plot3d.
fix whitespaces gr3/__init__.py.

Change-Id: I8a5e2a269b75733cb4413b898d48d8898b805aeb
Reviewed-on: https://iffwww.iff.kfa-juelich.de/review/3
Reviewed-by: Josef Heinen <j.heinen@fz-juelich.de>
Add preliminary support for GR surface option

Change-Id: Ica9ca99958720935fe55af75657def8247b759c5
Reviewed-on: https://iffwww.iff.kfa-juelich.de/review/4
Reviewed-by: Josef Heinen <j.heinen@fz-juelich.de>