Bug 35531: Add context for translating gender option "Other"

Bug 35531: Add context for translating gender option "Other"

To test:
* Apply patch
* Verify the option "Other" for gender is correctly displayed when:
  * Editing a patron record in the staff interface
  * Viewing the 'Details' tab of a patron in staff interface
  * Triggering a "duplicate" patron warning and looking at the details
    of the existing patron record
  * Self registering a patron in the OPAC
  * Viewing 'Personal details' tab in the OPAC for a registered patron
* If you are using ktd, run: gulp po:update --lang de-DE
* Verify string "gender" appears with the occurences of "Other"and
  "Other:" in
  misc/translator/Koha-messages.pot

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>