DRY Locus Map script uses common logic for saving files and writing to db

[rudokemper]

Goal

Closes #86.

What I changed

• locusmap.py now imports and utilizes save_data_to_file() and save_geojson_as_postgres()
• Additionally, I sought fit to also save the original Locus Map export file (e.g. GPX, CSV, KML) in file storage, since the user may want to access these files again e.g. to load in a specific software that doesn't support Postgres or GeoJSON.
• Added a utility function _make_geojson_features() used when transforming each of the Locus Map export formats to GeoJSON.