tasks #7402 Display time when option activated

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

This commit displays time in date field if option is checked.
It also validates submitted values with date+time.

Change-Id: Ifdded8e2b96e6369bc85ce33555c3de2113c61ff
Merge commit 'refs/changes/59/2959/7' of ssh://gerrit.tuleap.net:29418/tuleap into HEAD

* ssh://gerrit.tuleap.net:29418/tuleap:
  tasks #7402 Display time when option activated

Change-Id: I4c4f17cb2563b0a325c95e9d105f75534ffa2d53
This is Tuleap 7.4.99.14

Change-Id: I10475dc294745583ed17c74660711bc4b23e6f68