UWS service.

dates with no seconds, but also with no day or month. Representations in
days of year or weeks of year were not possible as well. Check out the
ISO8601Format class' Javadoc for more details.

[UWS,TAP] Fix timestamp format. Now, each returned date will expressed in UTC and using the ISO8601 format. Any given date is also expected in UTC (or with a time zone offset) and in ISO8601Format. These rules apply also for uploaded tables and for timestamp columns in a query result.