Add support for javax.persistence entity listeners

[iweinzierl]

I'd appreciate adding support for entity listeners like these via annotation:

• PrePersist
• PreUpdate
• PreRemove
• PostPersist
• PostUpdate
• PostRemove

An example could look like:

public class BookTitleValidator {
    @PrePersist
    public void validate(Book book) {
        // do validation magic
    }
}

@EntityListeners({ BookTitleValidator.class })
public class Book {
}