Removing duplicate dao method, refactoring Branch dao interface.

1. Removing duplicate dao method
Method void save(T entity) in ChildRepository is equal by implementation to void saveOrUpdate(T entity) in ParentRepository. It needed to removed duplicate functionality from parent repository as our parent extends child... (it's funny).

2. refactoring Branch dao interface (mapping bag to Collection).
According to Java Persistence With Hibernate note: Write the collection property with the java.util.Collection interface, and, on declaration, initialize it with an ArrayList of the JDK. Map the collection in Hibernate with a standard <bag> or <idbag> element. Hibernate has a built-in PersistentBag that can deal with lists; however, consistent with the contract of a bag, it ignores the position of elements in the ArrayList.