Changed start scripts

- only use the -d argument (for pylab) if the MPLBACKEND environment is set
  (Florian has already made a pull request: allow selecting the backend by
   setting the environment variable MPLBACKEND #3710)
- use -o (instead of -t) to specify the GKS workstation type
  (-t already used by Python to issue warnings about inconsistent tab usage)

Change-Id: If0baca0451671510350902da40b85f15b12078e2
Reviewed-on: https://iffwww.iff.kfa-juelich.de/review/109
Reviewed-by: Christian Felder <c.felder@fz-juelich.de>
Reviewed-by: Josef Heinen <j.heinen@fz-juelich.de>
Added two flags to control the clear/update bahavior of the matplotlib backend

Change-Id: Ib98b3d94e5073f793b602b1541ff6239d72cca5e
Reviewed-on: https://iffwww.iff.kfa-juelich.de/review/111
Reviewed-by: Josef Heinen <j.heinen@fz-juelich.de>