Add convertion type geojson

[mbolli]

Not fully tested yet, open for feedback.

I tested it with a 1 GB json file with the command python3.9 location_history_json_converter.py -f geojson -i -s 2021-05-01 Takeout/Location\ History/Location\ History.json test.geojson and it does what I need atm.

Possible optimizations:

• Remove geojson dependency
• Remove the need for the geojson_data variable where even with the -i option all coordinates are stored before writing them in _write_footer()
• Add feature like in converter type gpxtracks where a new track is created if coordinates differ by some measure