Add services usage in statistic plugin

* Move stats generated in IndicateurCodex.cgi into a dedicated section of the statistic plugin

Change-Id: I87a6089061f7b416e04fb3b9505c99880021c1d0
Merge commit 'refs/changes/49/449/3' of http://gerrit.tuleap.net/tuleap into stable

* http://gerrit.tuleap.net/tuleap:
  Add services usage in statistic plugin
This is Tuleap 6.1.99.1