use osmtogeojson instead of osm-and-geojson for OSM data import

here are the pros:
* stable (no crashes on incomplete OSM data)
* provides real OSM way-polygon detection
* properly supports OSM multipolygons (simple as well as complex multipolygons)
* well tested
* proven on overpass-turbo.eu
* faster(?)

cons:
* requires lodash
* doesn't provide geojson-to-osm conversion
update readme/libraries