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.
rules: 10 kibana dashboards is not enough

Default of 10 is a bit small and 20 won't hurt display.