- Permissions of 'gestion' app are correctly added to the staff groups
of associations.
- Add tests to ensure staff groups of COF and BDS are correctly setup.
- Shortcut functions are added to retrieve COF and BDS association.
BDS + COF
The permissions assignation is triggered by the `post_migrate` signal since the
permission table will only be populated after the migrations have been applied.
Fill bds.models with the required fields; add migration scripts, and a stupid
unittests that checks the model really works.
Note: old fields will migrate to datetime.now().
