Add map hover + pointer interactivity

Refactor to remove react-mapbox-gl dep, since our
use case is simple (just lots of layer declarations)
and the dependency adds complexity and larger bundles.

String geojson feature IDs don't get copied into the
vector tiles, thus can't be used for "feature state":
    mapbox/mapbox-gl-js#2716

Work around just uses osm object id via "promoteId".
It's possible but unlikely that two objects of different
types could share the same int id in a single diff. I
think the behavior in this case is just that both
elements with the same id would receive the same hover state.
The duplicate is likely offscreen.