Bug 8222 - make the zipcode no longer mandatory

Bug 8222 - make the zipcode no longer mandatory

Having the zipcode field mandatory by default is a bit annoying for
places where no one cares about it. This patch stops it being the case
on new installs.

Signed-off-by: Michael Davis <m.r.davis@cranfield.ac.uk>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
(cherry picked from commit fe5214ba5e326d23a2b689cd945012325107b9e0)

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