Bug 8012: default values for defaultSortField/defaultSortOrder NULL on install

Bug 8012: default values for defaultSortField/defaultSortOrder NULL on install

...which *looks* like "relevance/ascending" in the staff client, which doesn't make sense.
This patch initializes the values at "relevance/descending", which is a functional
combination.

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
(cherry picked from commit 5bc1246b6d1e3e25ff6c4b430bd698185ba876cc)

Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>