* i18n
* Vérification des variables dans les classes + throw exception
* tokens + ban system
* remember me
* htmlspecialchars => on users objects
* handle negative amounts
* Refactor load method to avoir load_* methods !

install.php :
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* TRUNCATE before CREATE TABLE in install.php

inc/Invoices.class.php :
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* Better way to store users in ? => reprendre cette partie
* Modify load() method to handle complex queries (such as WHERE date < DATE_1 AND date > DATE_2)
* Buyer as user object ?

Manage paybacks :
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