Add search-by-date CLI command

[zstumgoren]

Related to #100

Add a CLI command date-based searches to support case discovery.

Oklahoma's Oscn Site class already has a search_by_date method, and it appears we may be able to support the same in Wisconsin (#64).

We should hold off on this until we've added a few more platforms/states to ensure a stable API at the Site class layer.

As part of these changes, we'll need to address handling of logging (#100) in cli.py. We moved logging setup inside the search command as part of the Oklahoma refactor (#97) in order to simplify testing. We should refactor logging to set the log file and log level as cli options for all cli commands where relevant (e.g. search and the proposed search_by_date).