Powheg + MiNNLO samples are not understood correctly

[lmoureaux]

Datasets produced using Powheg's MiNNLO extension (e.g. this one) are tagged as NLO PH+P8. This should be NNLO.

The culprit is to be found here:

GrASP/api/samples_api.py

Lines 64 to 65 in 6e43893

	elif 'powheg' in name and 'pythia8' in name:
	short_name += ' NLO PH+P8'

A new special case for MiNNLO should to be added.