show billversion according to latest date

[derekeder]

once datamade/chicago-council-scrapers#9 is resolved, fetch the latest bill according to date instead of using first to determine the latest version:

https://github.com/datamade/chi-councilmatic/blob/main/chicago/models.py#L122

[fgregg]

so the elms data source does not have the information about the dates of different versions, so the best that we can do is try to infer ording from the names of the files (currently stored in the "notes" field).

however, we were improperly putting some attachements of docs into the billversion table isntead of the attachment files, so fixing that should help.