WebSearch: collection tree score as in next.

* Updates how the `score` value from `collection_collection` is used
  adopting next way, the lower the score the higher the position.

* 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>
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31: D202 No blank lines allowed *after* function docstring, found 1
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