fdo#76203 - use consistent titlecase for UI title labels

Change-Id: Icae67c083ca867c89cff7f9d5d44dbbe4aadcba9
Reviewed-on: https://gerrit.libreoffice.org/9858
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>