Add mapping between external Python types and CalendarIntervalType

We might consider adding support for at least collecting the results of queries containing interval types

spark.range(1).select(current_timestamp() - current_timestamp()).first()

and possibly a conversion in the opposite direction.

An obvious candidate would be datetime.timedelta which is mapped to net.razorvine.pickle.objects.TimeDelta, but semantics of these and CalendarInteval differs.