[WIP]: theory shift covmat comparison - updated

Created by: RosalynLP

Cleaner version carrying on from NNPDF/nnpdf#309

https://vp.nnpdf.science/bQCke9RZT4-eC4A7szF80g==/figures/plot_thcorrmat_heatmap_custom2.png This looks a bit weird to me - first it is missing FT DY relative to https://vp.nnpdf.science/NlltmlyWRRqCtSeJbi1xIQ==/, and second the correlations between different experiments look different to what we were previously seeing - I don't see why the upper left block of experiments should be so strongly correlated as they are just presented alphabetically - it seems as if maybe the labelling has been done wrong - any ideas of the cause of this? I am trying to debug but haven't spotted the issue yet.