Column identifiers added.
Calculation duplicates what is shown in WWV_FLOW_WORKSHEET_COLUMNS.
fix for column identifiers.
query was using column_id instead of display_order.
Merge commit 'a99d284043d5e55c15f6d82474c193a91c7c55ae' into issue10
Merge pull request #14 from commi235/issue10

Preliminary GROUP_BY enhancement for #10