Thanks to Sébastien Campion I rewrote the migration update. Now a SQL
file takes care of migrating and transforming all the data in the new
database. The bash script takes care of:

- deleting any existing tables in the Django database
- dump the current rails database and import it in the Django one
- apply the migration using the SQL script
- run the fake migration to take into account the current status of the
Django database

Signed-off-by: Matthieu Berjon <matthieu.berjon@inria.fr>