WebSearch: inverted collection scores

* Updates how the `score` value from `collection_collection` is used,
  the lower the score the higher the position.  Useful for running
  Invenio 1 and Invenio 2 out of the same database.  (PR #2058)

* Updates `democfgdata.sql` to use the new score.

* Provides an upgrade recipe to update the `collection_collection`
  relationships. It changes the score setting its value from 0 to the
  number of "son collections".

Signed-off-by: Esteban J. G. Gabancho <esteban.gabancho@gmail.com>
Tested-by: Tibor Simko <tibor.simko@cern.ch>