[WIP] Reader for new commondata

Created by: scarlehoff

We used #1526 as a scratchpad during the meeting so I'll leave it be and instead move here whatever is needed.

For now I've added just a jupyter notebook that reads the new commondata into pandas dataframes.

@enocera @Zaharid if you are ok with those df I'll port the rest (coredata.py and core.py, specs and so) using that as the underlying objects.

(why would the test pass here but not in #1500?)