Show processed values in preview

[sideeffect42]

Then I upload a CSV timesheet, I can only see the "raw" values as they are stored in the file in the preview.

This, unfortunately, makes some errors like kimai/kimai#4398 only visible after all rows have been imported into Kimai.
When importing many entries at once into a non-empty database this can lead to a lot of manual corrective effort.

Please consider improving the preview to show the processed values of the columns instead.