tasks #736:6 Handle mass change

This task is part of story #7354: finish story unsubscribe to artifact notification

Change-Id: I41e8526f8db50c7e958b7e9504bd42bbc2319717
tasks #7370 Enhance messages

This task is part of story #7354: finish story unsubscribe to artifact notification

Change-Id: I1a5b01f2f4ac8353eada19cc97624ab49801a3d2
Merge commit 'refs/changes/27/2927/9' of ssh://gerrit.tuleap.net:29418/tuleap into stable

* ssh://gerrit.tuleap.net:29418/tuleap:
  tasks #7370 Enhance messages
  tasks #736:6 Handle mass change
This is Tuleap 7.4.99.7

Change-Id: Ic4ad18b8f3d3b574abcd54bf11463cb1e771ccc7