adding option scale to groupPlot

[elenavernazza]

The option "scale" gives the possibility to scale each sample in groupPlot by a given factor.
If the same sample appears in different groupPlots, it can be scaled each time by a different factor.

Example:

k1 = 0.1; k2 = 0.5;
groupPlot['EFT_k1'] = {
'nameHR' : 'cqq11 = 0.1',
'samples' : ['sm','lin_cqq11','quad_cqq11'],
'scale' : {
'sm' : 1,
'lin_cqq11' : k1,
'quad_cqq11' : k1*k1,
}
}

groupPlot['EFT_k2'] = {
'nameHR' : 'cqq11 = 0.5',
'samples' : ['sm','lin_cqq11','quad_cqq11'],
'scale' : {
'sm' : 1,
'lin_cqq11' : k2,
'quad_cqq11' : k2*k2,
}
}