Create project structure with some business logic already implemented.

The structure is the following:

- common. Contains the basic types and exceptions of the system. Defines interfaces implemented by the JPA entities.
- core. EJB module with the business and data access logic. Uses JPA and stateless session beans, with local and remote interfaces, to build data access objects and services.
- core-remote. Contains the remote interfaces of the stateless session beans inside the core project.