Improve test lifecycle

In the context of the CAS-2, we should be able to trace the history of the tests. In particular, we need to know who validates a test when; currently we do not display when a test was validated.
In addition, a change in a "validated" test shall set back the validated attribute to false until someone reviews it and validates it again.
It would be convenient, in the comment section of the test to report the following actions (at least for tests used in accredited testing sessions): test has been validated, test has been updated

http://molene.kereval.com/tutos/php/bugtracking/bug_show.php?id=232175