tasks #6990 Handle citations in the answer

This is part of story #6301: reply to a follow-up comment by email

This is a first step for removing citation in mail received by the platform.
We can find and remove the citation itself, but not the sentence often added
by the MUA (e.g  "On Thu, Jun 05, 2014 at 04:52:17PM +0200, Tuleap wrote:" added by mutt)

So, we decided to keep this sentence and to replace the citation by
"[citation removed]"

Change-Id: I1f0c593dd2011b1c1d6bccd76ec73e70428fd37f
Merge commit 'refs/changes/91/2591/1' of ssh://gerrit.tuleap.net:29418/tuleap into stable

* ssh://gerrit.tuleap.net:29418/tuleap:
  tasks #6990 Handle citations in the answer
This is Tuleap 7.1.99.14

Change-Id: I58b240d4c5ea97bc8f233443408625df94b7108b