Made code compliant with moodle coding guidelines (again!)

Signed-off-by: Joseph Rézeau <moodle@rezeau.org>
2.5.7 (Build - 2013120200) ready for release.

Signed-off-by: Joseph Rézeau <moodle@rezeau.org>
CONTRIB-4778 :: In Conditional branching questionnaire, back navigation deletes previous answers.
CONTRIB-4779 :: Do not prevent from navigating to previous page when required questions on page are left unanswered.

Signed-off-by: Joseph Rézeau <moodle@rezeau.org>
CONTRIB-4785 :: Make List of individual anonymous responses available to the teacher (again)

Signed-off-by: Joseph Rézeau <moodle@rezeau.org>
CONTRIB-4788 :: removed the GROUP BY instruction which caused an error in Postgres and was un-needed.

Signed-off-by: Joseph Rézeau <moodle@rezeau.org>
CONTRIB-4789 :: Questions have required flag when they are not required

Signed-off-by: Joseph Rézeau <moodle@rezeau.org>