Bug 28936: Add sort1/sort2 to borrowers.json

Bug 28936: Add sort1/sort2 to borrowers.json

To Test:
1. Check the BorrowerMandatoryField and BorrowerUnwantedField system preferences, sort1 and sort2 cannot be hidden or required
2. Apply patch
3. Check the BorrowerMandatoryField and BorrowerUnwantedField system preferences again, you should see sort1 and sort2
4. Since sort1 and sort2 are now added to borrowers.json we must also check the system preferences PatronQuickAddFields & PatronDuplicateMatchingAddFields
5. They should both now include sort1 and sort2, check to make sure they work with these two system preferences
6. Look at the system preferences PatronSelfRegistrationBorrowerMandatoryField, PatronSelfRegistrationBorrowerUnwantedField, and PatronSelfModificationBorrowerUnwantedField
7. sort1 and sort2 should be disabled in these OPAC system preferences

This patch does not attempt to add sort1 or sort2 to the self reg or borrower mod pages. If they should be added, which I am not sure they should, we should do so in a seperate bug

Signed-off-by: Joonas Kylmälä <joonas.kylmala@iki.fi>
Signed-off-by: Emmi Takkinen <emmi.takkinen@koha-suomi.fi>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>