Add option to show Mapillary coverage

[roballey]

(A simple implementation was previously added but has been disabled to to issues with ogr2osm under Mint 22.2)

• Write my own simple converter for geojson (as downloaded from Mapillary) to OSM format (required by mkgmap). Base on convert_json_notes_to_osm in OSM_Notes.py
• Look at mapillary_coverage to identify which OSM highways have Mapillary coverage