Add real life Entities in tests

[welcoMattic]

Feature Request

Q	A
New Feature	no
RFC	yes
BC Break	no

Summary

As I see the 3 entities in TestBundle directory, those entities doesn't represent real life test cases. There's no association fields (OneToOne, OneToMany, ManyToMany), there's no Embedded fields ... So I think these cases are really missing to help people to understand how this bundle works and how to use it with complex data schema.

Thanks