speed up reverse lookup of place nodes

Add a special index that contains the place nodes buffered by their
respective area according to their search rank. This replaces the
maximum area search for place nodes and reduces drastically the number
of place nodes that need to be retrieved.

lib-sql/tables.sql

@@ -190,7 +190,6 @@ CREATE INDEX idx_placex_geometry_buildings ON placex
 
 -- Usage: - linking of similar named places to boundaries
 --        - linking of place nodes with same type to boundaries
---        - lookupPolygon()
 CREATE INDEX idx_placex_geometry_placenode ON placex
   USING {{postgres.spgist_geom}} (geometry) {{db.tablespace.address_index}}
   WHERE osm_type = 'N' and rank_search < 26