reactivate Robustness Process

[nilshempelmann]

Description

Robustness is a method to calculate the climate change signal strength of an ensemble

Flyingpigeon v.1.0 contained a robustness calculation:
https://github.com/bird-house/flyingpigeon/blob/1.0.x/flyingpigeon/robustness.py

robustness is vislualised on a map, with dots (robust) and haches (not robust signal).
#310

[nilshempelmann]

Papers:
http://www.tellusa.net/index.php/tellusa/article/view/23139
http://onlinelibrary.wiley.com/doi/10.1029/2011GL049863/abstract
http://www.nature.com/nclimate/journal/v3/n12/full/nclimate2051.html
http://www.nature.com/nclimate/journal/v3/n4/abs/nclimate1716.html

https://link.springer.com/article/10.1007/s00382-019-04831-z/figures/3?shared-article-renderer