Changes to make sure the hibernate mapping works for Firebird databases. New Hibernate configuration file.
Changed mappings and the consttruction of SessionFactory - now it uses the config file from within the project, not external file.

The reason of previous errors lies in the way the session factory was created. While configuration Players class was added and then session factory built. The class had already been defined in the config file and another adding might confuse Hibernate.
Mechanism for updateRank of a player within a given date added.
Changes to the logic of calculating the rank.

Comments TODO added.