add object types consistently to verbose debug output

although most of the time quite ambiguous, this is necessary in
some cases of the new overpass output modes where a node can
actually be a pseudo-object resulting from a way's "center"
geometry, for example.
add output info for special geometry features

features.properties.geometry=="center" for features resulting from
object with an overpass api center geometry
implement bounds geometry mode

constructed features are Polygons spanning over the object's
bounding box.

They are identifiable via: properties.geometry == "bounds"