mapBubble: Always convert to GeocodePlace to Place

https://bugzilla.gnome.org/show_bug.cgi?id=740937
Use osm-type+osm-id as index for places.

The osm id is only unique within a type of place such as
node, way or relation. We need the osm-type to make the index
unique.

https://bugzilla.gnome.org/show_bug.cgi?id=740937
overpass: Use the osm-type to look up data

https://bugzilla.gnome.org/show_bug.cgi?id=740937