Sort the Last visit time column using the date value and not its reprensetation

[GabLeRoux]

This is reproduced directly on the following page right now: https://editor.datatables.net/examples/dates/formatting.html

According to the documentation, it is totally possible to sort using a custom algorithm (and in this case, sort by actual datetime value):

https://www.datatables.net/plug-ins/sorting/

This blocks #22