rules: fix deletion of rules

Rules were deleted to early as they were still used to build the
changelog. Deletion is now donw once the update is finished.
rules: don't add link in deleted rules list

When displaying a changelog, the deleted rules are removed from the
database so we can't get to the rule detail page. This patch suppresses
the link in the array so user can't get to the 404 page.
scirius: work on migration to django 1.7

Migration are now part of django and south is not anymore available
for django 1.7. Recommanded update involve to move the migrations
directory to south_migrations. Recent south will then use that
directory instead of the migrations one which is now used by django.