make Calc function PERCENTRANK comply with ODF1.2

http://docs.oasis-open.org/office/v1.2/OpenDocument-v1.2-part2.html#PERCENTRANK
defines an optional 3rd argument. This hss now been added to the function.

Change-Id: Iaa0d990261be195ad0a4b6f6be7f76b9c084da40
Reviewed-on: https://gerrit.libreoffice.org/7747
Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>