* Don't cache the username
* JSON output => do index view
* API
* Reattribute all invoices / paybacks to unknown user when deleting a user ?
* Check that all is ok when deleting an invoice
* Use PHP constant in tpl instead of variables
* User groups
* cf TODO in files

Manage paybacks :
=================
* TODO : Payback system (class should be ok)
* TODO : Global payback