"Thousands Separator" and "Engineering notation" used the same checkbox,
 so help tips texts were the same.
This commit creates a second checkbox which is hiden/shown
 according to category selected

Change-Id: I804c2c7b4625497da8e423a952b357fbd8bbfa19
Reviewed-on: https://gerrit.libreoffice.org/24173Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>