[UWS] Fix the quote serialization.

The UWS-1.x standard defines the quote as an ISO-8601 date. UWS-Lib stores it
as a number of seconds (i.e. estimated job duration).

This fix ensures that this integer/long quote value is returned as a date.

Note: The backup and restoration processes are not affected by this change.
      The backup file format is still the same: a quote stored as a long value.