tasks #7413 wrong hour when setting time in field of NEW artifact

This task is part of story #7161 Create a date-time field

Adapt date time format to have a right interpretation of timestamp + fix a bug on
artifact creation for perTrackerId field (spotted when fixing this).

Change-Id: I87942cb8895e743d1263f58493d8faa895aeb688
Merge commit 'refs/changes/62/2962/2' of ssh://gerrit.tuleap.net:29418/tuleap into HEAD

* ssh://gerrit.tuleap.net:29418/tuleap:
  tasks #7413 wrong hour when setting time in field of NEW artifact

Change-Id: Id38f2dd92b36242e90b2479ebf3e7f3c6bb12238
This is Tuleap 7.4.99.16

Change-Id: Id26c5c1a94fa86fbb299736e26c8c1e1ff657cfb