Restructure the ENA picker to show studies more prominently ?

@nekrut mentioned that he's mostly browsing studies, since they contain metadata about what type of data (and how many runs) are part of the study.

Having a link in the dropdown of studies would be nice, but the UX of having clickable links there is a little odd.
Alternatives could be another mode where instead of rows corresponding to runs the rows would correspond to studies, and you could expand the rows to select runs from a study, in a sort of hierarchical display ?