Refactor Site OdysseySite to use standard interface

[zstumgoren]

OdysseySite currently requires a user to provide the start page URL for the site and a download directory (required for chromedriver configuration).

We should standardize the interface to match OK and WI by making the following changes:

• Only require place_id and dynamically look up the URL in sites_meta.csv. Any undiscovered Odyssey sites can be brought online by adding them to sites_meta.csv
• Make download_dir a kwarg with default set to standard cache dir (e.g. ~/court-scraper/cache/ga_dekalb).

This will set us up provide a simple, standard Site class that can be used to dynamically fetch the appropriate the Site class.