Bug 14652: change gender specification from "N/A" to "None specified"

Bug 14652: change gender specification from "N/A" to "None specified"

To test:

Edit a patron in the intranet, note that the gender options are "Female," "Male," and "None specified"

Setting "None specified" should result in the gender not being shown on the patron detail page (unchanged functionality)

In the opac, log in and click the "your personal details" tab, and note that the gender options are "Female," "Male," and "None specified"

Signed-off-by: Mirko Tietgen <mirko@abunchofthings.net>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@unc.edu.ar>