Implementacia unit testu pre LoanDAO

LoanDAOImpl.java: Bugfix v metode findLoansByFromTo()

Customer.java: Pridanie mapovania OneToMany medzi Customer a Loan (cez Collection<Loan> loans)

Impression.java: Pridanie mapovania OneToOne medzi Impression a Loan

Loan.java: Pridanie mapovania OneToOne a ManyToOne k entitam Customer a Impression

LoanTest.java: Implementacia unit testu pre LoanDAO interface