Bug 12728: Add StatisticsFields to sysprefs.sql

Bug 7955: [Statistics tab for Patron checkouts] introduced the pref
StatisticsFields but did not add it to the sql install file.

Test plan:
Run webinstaller or mysql ... < sysprefs.sql
Verify that the new pref is in your systempreferences table.

Signed-off-by: Bernardo Gonzalez Kriegel <bgkriegel@gmail.com>
Run webinstall, new syspref loaded.
No koha-qa errors.

Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>

installer/data/mysql/sysprefs.sql

@@ -378,6 +378,7 @@ INSERT INTO systempreferences ( `variable`, `value`, `options`, `explanation`, `
 ('StaffSearchResultsDisplayBranch','holdingbranch','holdingbranch|homebranch','Controls the display of the home or holding branch for staff search results','Choice'),
 ('StaffSerialIssueDisplayCount','3','','Number of serial issues to display per subscription in the Staff client','Integer'),
 ('StaticHoldsQueueWeight','0',NULL,'Specify a list of library location codes separated by commas -- the list of codes will be traversed and weighted with first values given higher weight for holds fulfillment -- alternatively, if RandomizeHoldsQueueWeight is set, the list will be randomly selective','Integer'),
+('StatisticsFields','location|itype|ccode', NULL, 'Define Fields (from the items table) used for statistics members','Free'),
 ('SubfieldsToUseWhenPrefill','','','Define a list of subfields to use when prefilling items (separated by space)','Free'),
 ('SubscriptionDuplicateDroppedInput','','','List of fields which must not be rewritten when a subscription is duplicated (Separated by pipe |)','Free'),
 ('SubscriptionHistory','simplified','simplified|full','Define the display preference for serials issue history in OPAC','Choice'),