tasks #7418: make datetime searchable and shown in the reports

- includes submitted on and last modified fields

Change-Id: I0ba6497f8e24eb34fa6fb71a29f389988875d4c7
Merge commit 'refs/changes/79/2979/5' of ssh://gerrit.tuleap.net:29418/tuleap into tuleap-stable-master

* ssh://gerrit.tuleap.net:29418/tuleap:
  tasks #7418: make datetime searchable and shown in the reports
Tuleap 7.4.99.21

Change-Id: Idf9a0694cb3db49eb621c32fb35eea29da306d25