Fix fdo#80432. Help entries for NORM functions

Write help pages for LOGNORM.DIST, LOGNORM.INV, NORM.DIST, NORM.INV, NORM.S.DIST and NORM.S.INV spreadsheet functions

Change-Id: I00f92dd339c6485f2f7b809f2e441241cde5a9d7
Reviewed-on: https://gerrit.libreoffice.org/9925
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>