[UWS] Make XML representation of jobs and joblists valid (with their XML schema), and particularly the nodes jobs, job and the error type (which should be written in lower-case).

[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.

[UWS,TAP] Review the exceptions and logs management + Add log file rotation (with a configurable rotation frequency)

[UWS] Improve the test of an URL: it may be null or the interesting part of it can be ; the two cases must be tested.