Add timestamp-based filter options to export command

[clausnagel]

To retrieve features that are now terminated but were valid at a given point in time in the past.

[thomashkolbe]

It would be good, if it can be chosen whether to refer that filter to the database valid time (creationDate, terminationDate) or the real-world valid time (validFrom, validTo). In this case, users can export the state of a city model reflecting how it was available / represented in the database at that time point or how the city really was like at that specific point in time.