related fdo#70998 change names in Navigator to plural

to be consistent with names of other items

Change-Id: I05a5484afde05f908f25df177d7e90f7991b84bb
Reviewed-on: https://gerrit.libreoffice.org/9942
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>