-- Some architectural changes --

1. Adding interface 'Identifiable' for domain classes with two methods -> getId(), setId(long)
2. Reduce size of the 'Dao'-code by placing general methods in GenericDao. It's high time =)
3. Change names of some methods in ClientDao: 'validateClient' to 'findClient', 'checkClientEmail' to 'findClientByEmail, 'checkClientLogin' to 'findClientByLogin' -> more accurate method names, I think.

 To be continued.