add y labels, integrate utils in filters and remove comma in sys names v2

[t7phy]

It seems there was an oversight on my part when opening #2020 that I hadn't noticed that nnpdf_data was already available as a standalone package that can be used while importing. This ofc allows (without any temporary breaking of filter files) to import utils from 1 place, as was agreed in CM. ATLAS_TTBAR_13TEV_HADR_DIF contains these utils and all the other ttb/jets/dis+j call whichever functions they need from here. This reduces code repetition and makes the review simpler.
To summarize:

• this PR adds y_label where we had discovered they were missing from my data implementations, here is a report to test the labels work: https://vp.nnpdf.science/MzdicX55Ti2M8PlOyp26Hg==/
• uncert. with names sys,* are changed to syst_*
• from validphys.commondata_utils is replaced with from nnpdf_data.new_commondata.ATLAS_TTBAR_13TEV_HADR_DIF.utils and I have explicitly checked rerunning the filters and they work.
• Utils for the new commondata #1693 and add y labels, integrate utils in filters and remove comma in sys names #2020 are now closed.

[Radonirinaunimi]

Thanks! LGTM now.