project structure improved, constructors created, minor code changes

[EltonC06]

Changes I've made:

1 - Project Structure: Now the project is divided in two packages, the application package and entities package.

2 - Constructors created: Constructors is a elemental key for classes you create, i added constructors to the "Cliente" and "Banco" classes.

3 - setContas removed: For a bank application isn't recommended to have the method setContas (to substitute a list of accounts by another) because is insecure. I removed the setContas method and added the addContas and removeContas, now you can add or remove an Account one by one, improving the security.