Fixing navbar z-index

Change-Id: I538b09e06dd9ad64274ecfec3e88098c295973e6
Merge commit 'refs/changes/89/1489/2' of ssh://gerrit.tuleap.net:29418/tuleap into stable

* ssh://gerrit.tuleap.net:29418/tuleap:
  Fixing navbar z-index

Change-Id: Ib56b906a4cde03e2443d579fd8d974a44370a42c
This is Tuleap 6.7.99.15

Change-Id: Id61dd2ca22329b9faa56a492f8eda3f488b2057d