record two values together to spreadsheet

[mathieu]

See files attached :

• in record-two-values-to-spreadsheet.ggb, the two values "c_1" and "poly1" are recorded separately to spreadsheet ; when "poly1" is undefined, it's recorded only once, so there's a gap between the rows where the two values are recorded
• in record-two-values-to-spreadsheet-list.ggb, the list {c_1,poly1} is recorded, so the rows where values are recorded are well linked

To have the same behaviour as record-two-values-to-spreadsheet-list.ggb, the user should be able to select both objects (c_1 then poly1), and then right-click > record to spreadsheet the selection.