Fix request #5450: login page customisation broken

Before 6.6, the customisation of intro on the login page was done through the
site-content .tab variable 'cookies' which, frankly speaking, was more a hack
than a foolproof solution.

Now we let the admin(or the marketing gal) define is own login
introductory text in an html file.

Change-Id: Ic3dccedd28af7b57b2bda60232fcb275a15a8ef8
Merge commit 'refs/changes/49/1349/1' of ssh://gerrit.tuleap.net:29418/tuleap into stable

* ssh://gerrit.tuleap.net:29418/tuleap:
  Fix request #5450: login page customisation broken

Change-Id: If67ac6246b2d8b896d940ea2d59254d24b751d02
This is Tuleap 6.6.99.6

Change-Id: Ia44a14aed4a86fde2105c55f7043464a3f5df8f5