place=postcode places are artificial places that collect addr:postcode
points for aggration. They should neither show up in the address nor
be searchable. That means that there is no need to index them at all.
Only let boundary=postal_code through which define correct areas for
postcodes.
The initial search and address rank is saved in a table
that is set up from a json configuration file. Ranks may
be assigned on a country level according to class and
type of the object. Special handling that depends on the
geometry or OSM type is still hard-coded in placex insert.
The new default config file mimicks the current assignment
as close as possible. A couple of exceptions have been
removed, most notably the exception for Irish townlands.
Many of the postcode nodes are actually derived from
incomplete addresses and are as such not even centroids.
Better let them only take part in the address computation
via the postcode table.
