Bug 33117: (follow-up) Rename preference

Bug 33117: (follow-up) Rename preference

As it's been requested that we keep the search defaults consistent, I
think this preference is better names DefaultPatronSearchMethod and
appear next to DefaultPatronSearchFields. This patch makes that change,
though actually applying it to the other search area's (outside of
autocomplete) has been left for another bug.

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>