Bug 22844: (QA follow-up) Build items.json for UniqueItemFields

Bug 22844: (QA follow-up) Build items.json for UniqueItemFields

Adding items.json, built from latest kohastructure.sql.
Control UniqueItemFields with this source file.
And add StatisticsFields.

Test plan:
Go to Preferences, play with UniqueItemFields.
Adjust StatisticsFields and look at patron record, statistics tab.

Moved-from: Bug 22867
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>