Fix issue with invisible chars while importing csv files

[tracyloisel]

Follow-up from the last PR opened and merged in August : https://github.com/pcreux/csv-importer/pull/107

The regexp /[^[:print:]]/ does not succeed to detect all invisible characters whereas the regexp /\P{Print}|\p{Cf}/ does.

If we strip each cell then we also need to remove invisible characters in each cell.