Consider adding a new helper that upsert things

[bjrmatos]

currently we have xlsxAdd for adding things and xlsxReplace to update them. however sometimes excel works weird, i mean when using office if i fill some cell but then decide to put empty content in there, the excel ended creating the row internally so that makes easy to forget if some row is already pre-created or not, this new helper can help in that case and avoid having to figure it out if the content exists or not in runtime.