tasks #6677: Introduce the "References" sidebar on the right (collapsed by default)

Change-Id: I244c7e098ab5807d2a41388826cbed56d0d338fc
Merge commit 'refs/changes/30/2330/3' of ssh://gerrit.tuleap.net:29418/tuleap into HEAD

* ssh://gerrit.tuleap.net:29418/tuleap:
  tasks #6677: Introduce the "References" sidebar on the right (collapsed by default)

Change-Id: I3a515440502e399d893621515f8fdb7ce3a06717
This is Tuleap 6.12.99.72

Change-Id: Id9a9ef8d4f11220b01dd8681a2835c76970cf320