tasks #7420: displaying hours in the date diffs in the following comments

- also uses language preference to display date in correct format

Change-Id: I7a5349d55de857050ec2810f2180575bf98f8af8
Merge commit 'refs/changes/80/2980/8' of ssh://gerrit.tuleap.net:29418/tuleap into tuleap-stable-master

* ssh://gerrit.tuleap.net:29418/tuleap:
  tasks #7420: displaying hours in the date diffs in the following comments

Change-Id: I7ef6f994e49381070b3facdb4e66b6f5d89e2e4e
Tuleap 7.4.99.22

Change-Id: I37fb42962f572993ac2839ac0991bcd2f4d3f22e