abu_chart plot labels

[fherwig]

when doing abu_chart plots with large isotope_database_txt the element labels become unreadable. use element names optionally as y labels (Falk has this in notebook somewhere already implemented)

[Samuel316]

Perhaps a new argument is needed that can either be True (by default), False, or a collection of the elements you wish to label on the plot?

abu_chart( ...element_names={True / False / ['Ne', 'K', 12, ...]} ...)