Bug 29822: Update 'DefaultPatronSearchFields' to a select list

Bug 29822: Update 'DefaultPatronSearchFields' to a select list

This patch updates the `DefaultPatronSearchFields` preference from
freetext expecting a comma delimited list of borrower fields to a
multi-select with a sensible list of fields available.

I opted to not use the Modal approach with all borrower fields listed as
I felt it made more sense to only expose a more limited subset of the
fields available to us.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>