Improve in-app library dropdowns

[Jaifroid]

As reported on Reddit here, it would be good to have a way to select ZIM archives with "all" in their filenames, as opposed to showing "All" entries).

Additionally, it would be useful to be able to select between "maxi", "mini", etc., or at least provide an explanation about what the differences are. Possibly a dropdown here is overkill because once an archive is selected by subject, language and/or date, usually the maxi, mini etc types are all shown grouped together in any case.