Customer entity, DAO interface, DAO interface implementation and unit test structure
Source code maintenance

App.java: removal of redundant imports

BookDAO.java: fix of tiny typo in javadoc

BookDAOImpl.java: removal of redundant imports

CustomerDAO.java: removal of useless javadoc

CustomerDAOImpl.java: removal of useless javadoc

LoanDAO.java: fix of tiny typo in javadoc

LoanDAOImpl.java: removal of useless javadoc

Impression.java: removal of redundant imports

Loan.java: unification of toString method output format with toString methods of other entities

ConditionType.java: removal of useless javadoc

StatusType.java: removal of useless javadoc

BookTest.java: removal of redundant imports

CustomerTest.java: removal of useless javadoc

LoanTest.java: removal of useless javadoc & removal of redundant imports