* i18n : i18n of errors in index.php and use a different template for each translation
* Don't cache the username
* JSON output

inc/Invoices.class.php :
========================
* Storage of users in ?!?

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

TODO :
======
* Add / Edit a bill

To test :
=========
* Connection form
* Remember me ?
* Edit notice
* Add / Edit user
* Change password
* Change settings